Multiple issues in the README.md file require editing

[KGBicheno]

I've made a fork to address the following issues in the README.md file:

• #Add Installation instructions #9
• #Add installation instructions in README file #17
• #Usage example is actually wrong #81

This is my first contribution to a project other than my own so there may be some steps in the process that I get a bit wobbly on. I've read the contribution guidelines and I'll push nothing rather than push with doubt.