Tell how to Create a Database in Error Message

Currently if you attempt to use a database that does not exist  you get an error:

```
PG::ConnectionBad FATAL:  database "db_error" does not exist
```

The solution is easy, create and migrate your database however new developers may not know these commands by memory. Instead of requiring the developer to search for a solution, tell them how to fix the problem in the error message:

```
ActiveRecord::NoDatabase: FATAL:  database "db_error" does not exist
Run `$ bin/rake db:create db:migrate` to create your database
```

Active Record should not know about `rake db:migrate` so this additional information needs to come from the railtie. Potential alternative implementation suggestions are welcome.

1 files changed, 7 insertions, 0 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 4e61a33fa1..6d130ab4d6 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   When connecting to a non-existant postgresql database, the error:
+    `ActiveRecord::NoDatabaseError` will now be raised. When being used with Rails
+    the error message will include information on how to create a database:
+    `rake db:create`
+
+    *Richard Schneeman*
+
 *   Do not raise `'can not touch on a new record object'` exception on destroying already destroyed
     `belongs_to` association with `touch: true` option