Update index.rst [Added how to install]

[purwowd]

No description provided.

[timhoffm]

Thanks for your contriution.

That's an install direct from the git repo.

The standard installation should be a released version:
pip install Cycler.

Installing from git is rarely needed and something for advanced users.

[purwowd]

Hi @timhoffm thanks for your response.

Of course standard installation using pip. This PR just for option how to install this package.

Thanks.

[timhoffm]

The text is too terse to be understandable:

• If we provide installation instructions, first and foremost we have to announce the standard pip install Cycler.
• Any alternatives given can only be additional and require context on when to use. - That said, I'm unclear about your usecase. Is this about trying the latest features? If so, most likely people still should use pip install . and not python setup.py install. Or is this for development? In which case this should be an editable install.