chore: improve php overwrite section

apps/docs/content/php/how-to/customize-runtime.mdx

@@ -55,13 +55,18 @@ When the custom runtime cache is used, Zerops doesn't create a prepare runtime c
 
 You can override PHP configuration directives by setting environment variables in your `zerops.yml` file.
 
-For example, to adjust PHP's maximum POST size limit, you would set the `post_max_size` directive like this:
+Here's an example of how to adjust PHP's `post_max_size` directive:
 
 ```yml
 zerops:
+  # define hostname of your service
   - setup: app
+    # ==== how to build your application ====
     run:
+      # REQUIRED. Sets the base technology for the build environment:
       base: [email protected]
+
+      # OPTIONAL. Defines the env variables for the build environment:
       envVariables:
         PHP_INI_post_max_size: 10M
 ```