Set directory permissions for Apache

Apache process doesn’t have write permissions for the /opt/git/
subdirectories. Restore the paragraph from this section:
https://git-scm.com/book/en/v1/Git-on-the-Server-Public-Access.

Signed-off-by: Vitaly Kuznetsov <[email protected]>

Author: vitalyq

book/04-git-server/sections/smart-http.asc

@@ -18,6 +18,13 @@ $ a2enmod cgi alias env
 
 This also enables the `mod_cgi`, `mod_alias`, and `mod_env` modules, which are all needed for this to work properly.
 
+You’ll also need to set the Unix user group of the `/opt/git` directories to `www-data` so your web server can read- and write-access the repositories, because the Apache instance running the CGI script will (by default) be running as that user:
+
+[source,console]
+----
+$ chgrp -R www-data /opt/git
+----
+
 Next we need to add some things to the Apache configuration to run the `git-http-backend` as the handler for anything coming into the `/git` path of your web server.
 
 [source,console]