Fixed article (an > a).
Merge pull request #25 from tstatler/patch-1

Fixed article (an > a) in opening sentence.
add public sharing content
PG build public sharing page may be set to inaccessible
minor rewording
removed duplicate word
enable debug section
bootstrap error content
expose & rename PG Build error content
rewrite PG Build error section
prevent every 'PhoneGap Build' instance from autolinking
nest topics in their own dirs, matching other doc
fix link to PG Build API