Update README.rst to specify secure protocols where possible

Update README.rst to specify secure protocols where possible

Change git clone commands to specify https instead of git or http.
GitHub has removed support for the git protocol
(https://github.blog/changelog/2022-03-15-removed-unencrypted-git-protocol-and-certain-ssh-keys/)
and http accesses will normally redirect to https.

Update links to use https where possible: all the sites with updated links
automatically redirect http accesses to https.

Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
Link: https://lore.kernel.org/r/20220711025547.11917-1-rebecca@bsdio.com
[axboe: fix git.kernel.dk location]
Signed-off-by: Jens Axboe <axboe@kernel.dk>