Add some friendlier defaults to database.yml

Actually let people get going out of the gate without forcing them to
puzzle out database.yml configurations. Also gives some hints on how to
set up a database.

Today, if you merely copy and paste from database.yml.example, you'll
get yelled at:

````
$ ./msfconsole -L -y config/database.yml
[-] No database definition for environment production
````

config/database.yml.example

@@ -1,4 +1,10 @@
 # Please only use postgresql bound to a TCP port.
+# Only postgresql is supportable for metasploit-framework
+# these days. (No SQLite, no MySQL).
+#
+# To set up a metasploit database, follow the directions hosted at:
+# https://fedoraproject.org/wiki/Metasploit_Postgres_Setup (Works on
+# essentially any Linux distro, not just Fedora)
 development: &pgsql
   adapter: postgresql
   database: metasploit_framework_development
@@ -9,6 +15,12 @@ development: &pgsql
   pool: 5
   timeout: 5
 
+# You will often want to seperate your databases between dev
+# mode and prod mode. Absent a production db, though, defaulting
+# to dev is pretty sensible for many developer-users.
+production: &production
+  <<: *pgsql
+
 # Warning: The database defined as "test" will be erased and
 # re-generated from your development database when you run "rake".
 # Do not set this db to the same as development or production.