[NaCl Docs] Add "Running" and "Debugging" docs.

These are ported directly from devsite with no changes.

R=eliben@chromium.org

Review URL: https://codereview.chromium.org/24360015

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226022 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226022