Improve Quick Start document

[fabiocarvalho777]

Improve Quick Start document by:

1. Adding a human readable instructions list explaining how to convert the WAR application to Spring Boot.
2. Adding a copy of the sample transformation template class source code to the document (plus a link to it in GitHub).
3. Adding a section about how to run it from an IDE (including steps about how to add sample-extension to the class-path, and the corner cases depending on which IDE is being used)
4. Adding a note warning users to be careful to not build the sample-app project before running butterfly, or clean it (mvn clean), if it has been built already.