Use https instead of http where possible Many of the external links found in the notmuch source can be resolved using https instead of http. This changeset addresses as many as i could find, without touching the e-mail corpus or expected outputs found in tests.
README.rst: typo/wording fixes It occurs that hardcoding the URL will not make sense in forks. Mind you, the whole README won't make much sense in forks.
doc: add README.rst especially for github Apparently README.rst overrides README, so this will show up instead of our generic README on github. If the user is already on github, then clicking a link for more information is not a hardship.