Added a developer's guide

[JJ-Shapiro]

Hi - I'm Joe, currently developing the Framework 16 to MXM adapter. Lots of people have been contacting me recently asking for help setting up/designing new modules, as there isn't a huge amount of information online about how to develop them.

I've sketched up this brief example of something that would be useful as a reference for the developer community, based partially off already available information, (just compiled into one place), and partially off personal experience developing for the Framework.

I'd be really happy to correct any kind of formatting/content errors you'd like, but I'd love to see something like this be publicly available - and easy to find! for people hoping to contribute to the community.

Please do get in touch if anything needs to be amended.

Thanks for all your help with this, JJ Shapiro