Update project-setup.mdx (wix#3995)

To clarify setup, as currently it's very easy for your eyes to just see the google() portion and put it in the wrong place. Spent 2 days struggling with this, and others have too. wix#3973

docs/introduction/project-setup.mdx

@@ -148,6 +148,7 @@ patch or create if they are missing:
 ### 4.1. Patching build scripts
 
 Open your main build script and apply the suggested changes:
+⚠️ New android projects won't have an allprojects {} section, so it will need to be added.
 
 ```diff title="android/build.gradle"
  buildscript {