Various cleanups to Ubuntu installation instructions:

* Avoid editing /etc/apt/sources.list add nginx repo, instead create
  /etc/apt/sources.list.d/nginx.list

* Avoid editing /etc/nginx/nginx.conf, instead put server_name_hash_buckets
  setting into discourse.conf

* Proper-case Discourse when it is referring to the product name, so that all
  the lowercase references are to the user created during the installation

docs/INSTALL-ubuntu.md

@@ -125,7 +125,6 @@ Install RVM
     # As 'discourse'
     # Install RVM
      \curl -s -S -L https://get.rvm.io | bash -s stable
-
     # Refresh your profile
     . ~/.rvm/scripts/rvm
 
@@ -231,6 +230,7 @@ site:
 
 Edit /etc/nginx/conf.d/discourse.conf
 
+- add: `server_names_hash_bucket_size 64;` at the beginning
 - edit `server_name`. Example: `server_name cain.discourse.org test.cain.discourse.org;`
 - change socket count depending on your NUM_WEB count
 - change socket paths if Discourse is installed to a different location