Removing duplication by putting everything in the readme. Allow us to close issues that deviate from the guidelines.

Better header and detail why you need two times the storage. Also moving memory and storage to the bottom, OS is more important.

Allow connection to Redis via unix socket, using
unix:/var/run/redis/redis.sock for example.

Default behaviour does not change, except that the full Redis URL must
be configured, with redis:// for tcp or unix: for unix socket.

Remove prompt $ from code line for uniformity

changed installation overview list step #4
Gitolite -> GitLab shell 

Added creation of pids directory to fix #2995, replaced deprecated nginx init.d command with service one, some more clean-up

Made it a bit clearer what step 5 is for to stop people skipping it. This time with a relative link.