.gitattributes: .doc are text files
Typo: remove extra space before colons
Doc: proofread beginner's documentation

Update source repository (github).
Advertise the configure script, it is simpler for beginners than
running cmake.
Update FirstApp.doc with current myapp.cpp.
Doc: proofread quick reference guide
Merge pull request #291 from dbarbier/feature/proofread-doc

Proofread  documentation