Detail how we collaborate with external labs, including funding

[adamltyson]

It may not be clear how we work with labs outside SWC/GCNU. It might be worth outlining the available "models", something along the lines of:

• If you need a feature, and it's near the top of our priorities, you could wait for us to build it, or help us out :)
• If you need a feature, and it's on our priority list, but not at the top, you could:
  • Raise a PR yourself
  • Discuss with us and ARC about working with ARC devs to prioritise the feature
• If the feature is large, discuss with us about applying for some dedicated funding

[adamltyson]

The NIU/Keshavarzi/ARC collaboration could be used as a nice example. At some point we should probably blog about it.