ROSES - FPrime platform and toolchains

[kubiak-jpl]

Description

Document creating custom platform and toolchain files. Here are some questions that I have

• What are the differences between platforms and toolchains?
• What information belongs in one vs. the other? There is some good information in the provided templates already
• How to point a cross-compile build to different platforms?
• Are there expected compiler flags that should be defined in the platform vs. the toolchain?

Deliverables (completed before closing issue):

• Select deliverable type
  • Reference
  • User Guide
  • How-To
  • Tutorial
  • Other (tool, fill-in, etc)
• Create documentation
• Create example in examples repository
• Pass expert review
• Pass user review