Add a section to CONTRIBUTING.md that includes all the necessary features of a new language generator

[jhowlett-scottlogic]

To facilitate the development of new languages, there needs to be a list of requirements of each generator to first ensure the generator is possible to complete and also to ensure the generator will be production quality.

Include:

• Set up a testing that can run the cucumber test against language generator (no point adding a new language if that language has no implementation of Gherkin notation)
• Add apiTemplate array to package.json that includes all files that need to be generated per tag