GetTor help message could be more helpful

The GetTor email help message says

This is how you can request a tor browser bundle link.

Send an email to: gettor@torproject.org

In the body of the email only write: <operating system> <language>.

We only support windows, osx and linux as operating systems.

Some things we can add:

• instructions on how to verify the signature
• instructions on how to get bridges?