Added installation steps for Python 2.7 and go 1.10+

[aaronjohnson92]

If you'd prefer this setup differently just let me know and I'll re-format to your specifications.

[alanjds]

Thanks for your effort, @aaronjohnson92.

Had you tried Grumpy on Windows? It is not being tested by the CI. I even doubt that it can build on non-POSIX platforms. Can you provide feedback on this?

About the text: I start to think that the README is already too big. Maybe just informing the pre-requisites and linking to external pages for instructions, or provide another file (PREREQUISITES ?) would be better. What do you think?

[aaronjohnson92]

I've updated the readme.md file to include links to the official installation documentation for the pre-requisites. I cut down more than half of what I submitted the first time. If you have any suggestions or preferences as to how it could be formatted I'm more than happy to change it to fit that!

Also, the longer section is the installation instructions for Python2.7 on linux. Only because some flavors don't bundle 2.7 anymore and default to 3.5+ which has the unfortunate consequence of the default python path being set to 3.5+ rather than 2.7 which could make the installation process some what confusing for newer users.

[alanjds]

Thanks @aaronjohnson92