INSTALL.md: fix pip instructions.

* pip has `--user`, `--install-option` just confuses people.
* pip user installation happens by `pip install limnoria --user`.
INSTALL.md: Tell pip to install from git master.

[SKIP CI]
INSTALL.md: clone using HTTPS instead of GIT.

GitHub seems to be removing the `git://` links. Changing to `https://`
in case they are going to discontinue `git://`.

[SKIP CI]
INSTALL.md: fix copy-pasting.

[SKIP CI]
Merge pull request #715 from Mkaysi/install

INSTALL.md: fix instructions.