Update command to execute as git user

doc/install/installation.md

@@ -147,7 +147,7 @@ Fix the directory permissions for the repositories:
     # Make sure the repositories dir is owned by git and it stays that way
     sudo chmod -R ug+rwX,o-rwx /home/git/repositories/
     sudo chown -R git:git /home/git/repositories/
-    find /home/git/repositories -type d -print0 | sudo xargs -0 chmod g+s
+    sudo -u git -H find /home/git/repositories -type d -print0 | sudo xargs -0 chmod g+s
 ## Add domains to list to the list of known hosts