Signin: Add section to note the site is free

The fact that the site is free is one of the
stronger pitches that people seem to take note
off when discussing Circle Blvd, so add this to
the signing page.
Signin: Describe the sign-up process

Add a description to the sign-up section of the
sign-in page. Make the placeholders less 
ambiguous. Make the language softer, as the word
"create" can be intimidating, so use "start"
instead.