Correct a few grammar issues in gitrepository-layout.txt and also
rewords a few sections for clarity.
Remove references to using http-fetch without -a to create a broken
repository.
Mark a few areas of the repository structure as legacy.
Signed-off-by: Ben Walton <bwalton@artsci.utoronto.ca>
Signed-off-by: Junio C Hamano <gitster@pobox.com>