Merge pull request #846 from spacewander/note

doc: add a note about the package maintainer.

Author: spacewander

Installation.md

@@ -11,6 +11,9 @@ Those dependencies are listed below:
 
 ## Installing with a package manager
 
+Note that only Homebrew package is maintained by the git-extras developers directly.
+Other packages are maintained by the distribution's packagers or third-party volunteers.
+
 ### Debian
 
 ```bash