Document how to make a Lens release

[timakro]

• Add a page to the "Development" section of the Lens Book that lists the steps required to make a new release
• Mention that you should create a migration guide if there are breaking changes
• Nice to have:
  • Extend index.html/dev.ts to include more functionality
  • Add a testing protocol to the Lens Book that describes what should be tested before making a release: I don't think it must go into detail, more something like test that all the input types still work and appear in the AST that gets sent out, make sure all the graph types work, etc.