Merge branch 'clarify_lfs' into 'master'

Clarify LFS configuration

A user on Twitter was confused (rightfully so) because LFS admin docs suggest you must set a storage path. In fact, Omnibus defaults to a very sane location. Add a comment to the snippet outlining the default.

See merge request !3388

doc/workflow/lfs/lfs_administration.md

@@ -23,6 +23,10 @@ In `/etc/gitlab/gitlab.rb`:
 
 ```ruby
 gitlab_rails['lfs_enabled'] = false
+
+# Optionally, change the storage path location. Defaults to
+# `#{gitlab_rails['shared_path']}/lfs-objects`. Which evaluates to
+# `/var/opt/gitlab/gitlab-rails/shared/lfs-objects` by default.
 gitlab_rails['lfs_storage_path'] = "/mnt/storage/lfs-objects"
 ```