Add small improvement to Manifest import feature docs

1. Add link to manifest used by AOSP
2. Mention both Android and AOSP keyword for better search
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

doc/user/project/import/manifest.md

 # Import multiple repositories by uploading a manifest file
 
 GitLab allows you to import all the required git repositories 
-based a manifest file like the one used by the Android repository.
+based a manifest file like the one used by the [Android repository](https://android.googlesource.com/platform/manifest/+/2d6f081a3b05d8ef7a2b1b52b0d536b2b74feab4/default.xml).
+This feature can be very handy when you need to import a project with many repositories like Android Open Source Project (AOSP).
 
 
 >**Note:**