Updating README.md to have a table of contents

for https://bountify.co/create-table-of-contents-for-readme-using-github-flavored-markdown , used https://github.com/aslushnikov/table-of-contents-preprocessor and cleaned up a the generated TOC using regular expressions
Merge pull request #1 from marks/patch-1

Updating README.md to have a table of contents