Split Windows and Linux instructions apart
Merge pull request #94 from townxelliot/rewrite-getting-started-1284

Split Windows and Linux instructions apart
Add note to FAQ about support for desktop platforms
Update build instructions

This addresses https://crosswalk-project.org/jira/browse/XWALK-1307
and https://crosswalk-project.org/jira/browse/XWALK-1059.