Update en-US.md

Minor modifications and clarifications - Jishnu (moz legal)
Merge pull request #22 from jishnu/patch-1

Update en-US.md
Updating Mountain View Office address
Merge pull request #23 from retornam/mtvaddressupdate

Updating Mountain View Office address
update date to today; a=mika
Update en-US.md

Updating with some clarifications and rewrites
Merge pull request #24 from jishnu/patch-2

Update en-US.md
Fix poor grammar in English and untranslated Marketplace TOU (bug 985561)
Fixed grammatical error 

changed "allowing" to "allows" per Bug 985561
Merge pull request #25 from chuckharmston/985561-typo

Fix poor grammar in English and untranslated Marketplace TOU (bug 985561)
Update en-US.md
Merge pull request #26 from GeoffPiperMZ/patch-3

Update en-US.md
reformatted to match style of Firefox OS PN

Added bullets, line breaks, topic sentences, word headings, and copy changes per JM review
reformatted for consistent style
reformatted for consistent style
Add IDs, fix garbage characters