Implement and Document magento2:generate:service-contract Command

[astorm]

We need documentation for the magento2:generate:service-contract command.

A skeleton entry for this command can be found in the docs/ folder. Use grep, ack, (or your search tool of choice), etc. to find the file where magento2:generate:service-contract should be documented. If you can't find this command, pick a file and/or ask about it in the comments below.

Documentation should include

1. An example of an interactive invocation (no argument)
2. An example of a an argument based invocation
3. A basic explanation of what this command does ("adds a model to the system")
4. An explanation of every possible file that might be created (Model/Thing.php, etc/frontend/someconfig.xml, etc)
5. If you need use an example module name, use Pulsestorm_Pestle for consistency
6. Links to existing documentation for the feature -- preference given to documents on alanstorm.com, but almost anywhere on the internet is appropriate, so long as the information is accurate.
7. Leave the output from help in your docs -- include your new stuff below this

Once you've documented this feature, make a PR against the master branch of the astorm/pestle repository.

If you have any question please ask below, but also be bold. Documentation is an iterative process so it's better to take a first crack at something and then ask questions about what you have.

Also if you disagree with something above -- come at us. :) The seven guidlines above are just that -- guides. If you have a better idea we want to hear about it.

[astorm]

Dropping this from the milestone -- the magento2:generate:service-contract is barely even an alpha command and not something that's ready fro prime time. Some base minimum viable command would need to be implemented.