Remove Tl;DR from install doc

Remove "TL;DR" reference from install doc.

doc/install/relative_url.md

@@ -24,8 +24,8 @@ Note that by changing the URL on an existing GitLab installation, all remote
 URLs will change, so you'll have to manually edit them in any local repository
 that points to your GitLab instance.
 
-The TL;DR list of configuration files that you need to change in order to
-serve GitLab under a relative URL is:
+The list of configuration files you must change to serve GitLab from a
+relative URL is:
 
 - `/home/git/gitlab/config/initializers/relative_url.rb`
 - `/home/git/gitlab/config/gitlab.yml`