fix readme to add helpful info on global install

This note will avoid people being confused when using the CLI who are less familiar with using global NPM installs.
remove ugly ```bash gitHub highlighting 

it was ugly in the readme
fix lowercased letter

a stray "i" went uncapitalized in the title of a section
Merge pull request #69 from DelmerGA/master

add helpful notes to readme
Make the docs DRY
Update README.md
Use umzug as migrator engine
Add task which migrates to new migration structure