Update for the LDAP auth wiki page
Created by: patthoyts
It seems we cannot raise merge requests for wiki pages. I've written some extra details about why someone might want to use LDAP as well as describing how it works. This is available for merging somehow from https://github.com/patthoyts/gitlabhq/wiki/Setting-up-ldap-auth
If someone knows a better way to provide wiki changes - please create a "How to contribute wiki edits" to go with the "Contributing" section in the wiki. Thanks.