fix build

add CONTRIBUTING.md to Makefile.am and license.skip
remove duplicate file from Makefile.am

This closes #184

Signed-off-by: Alexander Shorin <kxepal@apache.org>
Fauxton: remove caching
encoded attachment name
spell checking my-first-couchdb-plugin's README
update opening note
update clone command to clone from github repo

since this already works on main couchdb.