Add --region to command lines, and mention in Performance

[nielm]

Add a --region command line arg with the default value of us-central1 as an indication to users where they should change it (for #72)

Also add an entry in performance tips on regions.

Also correctly format and punctuate the markdown in the performance tips section.

[EricBeach]

Since the presubmits won't pass here, I'm handling this in #82

[nielm]

handled in #82