[Docs] Updating repository preview info (#2890)

This pull request updates the "Quick Start Guide for Developers"
documentation to improve clarity, add practical instructions, and expand
coverage of previewing pull requests and branches in Playground. The
most important changes are grouped below:

**Previewing Pull Requests and Branches:**

* Added detailed instructions for previewing repository code in
Playground using either `git:directory` or direct `.zip` URLs, including
a JSON Blueprint example and explanation of CI requirements.
* Introduced a new section on previewing WordPress Core and Gutenberg
branches or PRs using Query API parameters, with concrete URL examples
for trunk and PR previews.

**Content and Clarity Improvements:**

* Updated the description metadata for the guide to reflect better
coverage of embedding WordPress, installing plugins, previewing PRs, and
using Playground APIs.
* Reworded plugin and theme installation instructions for clarity and
conciseness.
* Revised compatibility testing environment instructions to emphasize
configuring PHP and WordPress versions for plugin testing in Playground.

**Blueprints API Update:**

* Updated the Blueprints API example for importing WXR files to use the
`file` property instead of `pluginData` for resource URLs.

Author: fellyph

packages/docs/site/docs/developers/03-build-an-app/01-index.md

@@ -1,6 +1,7 @@
 ---
 title: Quick Start Guide for Developers
 slug: /developers/build-your-first-app
+description: Practical guide to embedding WordPress, installing plugins, previewing PRs, and building apps with Playground APIs.
 ---
 
 # Quick Start Guide for Developers
@@ -39,8 +40,7 @@ Learn more about each of these APIs in the [APIs overview section](/developers/a
 
 import ThisIsQueryApi from '@site/docs/\_fragments/\_this_is_query_api.md';
 
-You can install plugins and themes from the WordPress directory with only URL parameters. For example this iframe would come with the `coblocks` and `friends` plugins preinstalled as well as the `pendant` theme.
-
+You can install plugins and themes from the WordPress directory with only URL parameters. This iframe preinstalls the `coblocks` and `friends` plugins and the `pendant` theme.
 <ThisIsQueryApi />
 
 ```html
@@ -72,7 +72,7 @@ You can still showcase it on Playground by using [JSON Blueprints](/blueprints).
 		},
 		{
 			"step": "importWxr",
-			"pluginData": {
+			"file": {
 				"resource": "url",
 				"url": "https://your-site.com/starter-content.wxr"
 			}
@@ -85,15 +85,44 @@ See [getting started with Blueprints](/blueprints/getting-started) to learn more
 
 ## Preview pull requests from your repository
 
-See the [live example of Gutenberg PR previewer](https://playground.wordpress.net/gutenberg.html).
+You can preview repository code two ways: directly with `git:directory`, or by pointing to a `.zip` from your CI pipeline. Here's the `git:directory` approach using [Blueprints](/blueprints):
 
-You can use Playground as a Pull Request previewer if:
+```json
+{
+	"steps": [
+		{
+			"step": "installPlugin",
+			"pluginData": {
+				"resource": "git:directory",
+				"url": "https://github.com/my-user/my-repo",
+				"ref": "refs/pull/1/head",
+				"refType": "refname"
+			},
+			"options": {
+				"activate": true
+			},
+			"progress": {
+				"caption": "Installing plugin from my-user/my-repo PR #1"
+			}
+		}
+	]
+}
+```
+
+In the code above, it will install a plugin from a repository located at the `url`, and the reference to find the branch is `refType`; in this case, it will use `refname`, but it can also use `branch`, `tag`, and `commit`.
+
+:::tip
+You can automate this process using the [GitHub Action to generate preview links](/guides/github-action-pr-preview), which will help streamline the process.
+:::
 
--   Your WordPress plugin or theme uses a CI pipeline
--   Your CI pipeline bundles your plugin or theme
--   You can expose the zip file generated by your CI pipeline publicly
+Loading a `.zip` file is another alternative for previewing your project. See the [live example of Gutenberg PR previewer](https://playground.wordpress.net/gutenberg.html).
 
-Those zip bundles aren't any different from regular WordPress Plugins, which means you can install them in Playground using the [JSON Blueprints](/blueprints) API. Once you exposed an endpoint like https://your-site.com/pull-request-1234.zip, the following Blueprint will do the rest:
+To use Playground as a PR previewer, you need:
+
+-   A CI pipeline that bundles your plugin or theme
+-   Public access to the generated `.zip` file
+
+Those zip bundles aren't any different from regular WordPress Plugins, which means you can install them in Playground using the [JSON Blueprints](/blueprints) API. Once you expose an endpoint like https://your-site.com/pull-request-1234.zip, the following Blueprint will do the rest:
 
 ```json
 {
@@ -154,9 +183,17 @@ blueprint={{
 	]
 	}} />
 
+### Preview WordPress Core and Gutenberg Branches or PRs
+
+You can preview specific pull requests from WordPress Core and Gutenberg repositories using Query API parameters. Gutenberg branches also have an alternative to preview them with the parameter `gutenberg-branch`. This is useful for testing the latest trunk changes or specific feature branches without creating a PR.
+
+-   Preview a specific WordPress Core PR: `https://playground.wordpress.net/?core-pr=9500`
+-   Preview a specific Gutenberg PR: `https://playground.wordpress.net/?gutenberg-pr=73010`
+-   Preview the Gutenberg trunk branch: `https://playground.wordpress.net/?gutenberg-branch=trunk`
+
 ## Build a compatibility testing environment
 
-A live plugin demo with a configurable PHP and WordPress makes an excellent compatibility testing environment.
+Test your plugin across PHP and WordPress versions by configuring them in Playground. This helps you verify compatibility before release.
 
 With the Query API, you'd simply add the `php` and `wp` query parameters to the URL: