install.rst: add pip
install.rst: fix things with help from @ProgVal .
install.rst: fix clode blocks with help from @ProgVal
install.rst: fix typo.
install.rst: Do changes suggested by @ProgVal & add upgrading with pip.
Merge pull request #5 from Mkaysi/install.rst

Document installing with pip.
Fix typoes.
Remove the install guide section for using Git.
Fix syntax.