Documentation: Add Caveats section for MAMP (#25444)

* Getting started: MAMP server: Caveats

* MAMP docs: Merge Caveats with E2E section

docs/contributors/getting-started.md

@@ -59,7 +59,11 @@ See the [relevant section in `wp-env` docs](https://github.com/WordPress/gutenbe
 
 ## Using MAMP
 
-You can also develop with MAMP by cloning and installing Gutenberg as a regular plugin in a WP install, but you'll require some extra configuration to be able to run the e2e tests.
+You can also develop with MAMP by cloning and installing Gutenberg as a regular plugin in a WP install, but it comes with its caveats and will require some extra configuration to be able to run the e2e tests.
+
+### E2E testing
+
+Ensure that Gutenberg's E2E-dedicated plugins are available in the WordPress installation's `plugins` directory. For this, you can either copy the plugins as a whole, or you can create links from the Gutenberg project directory. This method is better in the long run but requires that link following be enabled. See section _Linking to other directories_ below, then come back and follow these instructions:
 
 Change the current directory to the plugins folder and symlink all e2e test plugins:
 
@@ -73,6 +77,35 @@ You'll need to run this again if new plugins are added. To run e2e tests:
 WP_BASE_URL=http://localhost:8888/gutenberg npm run test-e2e
 ```
 
+### Caching of PHP files
+
+You'll need to disable OPCache in order to correctly work on PHP files. To fix:
+
+- Go to **MAMP > Preferences > PHP**
+- Under **Cache**, select **off**
+- Confirm with **OK**
+
+### Incoming connections
+
+By default, the web server (Apache) launched by MAMP will listen to all incoming connections, not just local ones. This means that anyone on the same local network (and, in certain cases, anyone on the Internet) can access your web server. This may be intentional and useful for testing sites on other devices, but most often this can be a privacy or security issue. Keep this in mind and don't store sensitive information in this server.
+
+While it is possible to fix this, you should fix it at your own risk, since it breaks MAMP's ability to parse web server configurations and, as a result, makes MAMP think that Apache is listening to the wrong port. Consider switching away from MAMP. Otherwise, you can use the following:
+
+- Edit `/Applications/MAMP/conf/apache/httpd.conf`
+- Change `Listen 8888` to `Listen 127.0.0.1:8888`
+
+### Linking to other directories
+
+You may like to create links in your `plugins` and `themes` directories to other folders, e.g.
+
+- wp-content/plugins/gutenberg -> ~/projects/gutenberg
+- wp-content/themes/twentytwenty -> ~/projects/twentytwenty
+
+If so, you need to instruct Apache to allow following such links:
+
+- Open or start a new file at `/Applications/MAMP/htdocs/.htaccess`
+- Add the following line: `Options +SymLinksIfOwnerMatch`
+
 ## On A Remote Server
 
 You can use a remote server in development by building locally and then uploading the built files as a plugin to the remote server.