Add Installation instructions

[bcambel]

It's handy to add Install instructures to the Main README.md page; such as

Installation

It's highly suggested to create a virtual environment to deal with the site-packages.
Please use virtualenvwrapper or virtualenv

virtualenv venv -p python3.6
# or 
mkvirtualenv textpipe -p python3.6
# install the packages
pip install -r requirements.txt

[anneschuth]

Installation for users you mean? That would be pip install textpipe

[jinxcat]

It would be handy to have both end-user and developer installation instructions, with some sane green-path examples to run.

[bcambel]

so the example I give is for developers, but as @jinxcat said could be both ways

[KGBicheno]

I've made a fork and pull request to fix this and will put it up for review unless something goes wrong.