[DOC] Add platform support matrix

[bdice]

We would like to add a version support chart, based on the ideas raised in #466.

We have the following goals:

• Communicate supported versions for the following for each RAPIDS release:
  • CUDA Toolkit/Runtime requirements
  • CUDA Driver requirements
  • Python
  • glibc
  • Compute capabilities (architectures) built/shipped in major RAPIDS products
• Declare the data for the above in a declarative way (YAML, JSON)
  • Current plan is to add platform support information to https://github.com/rapidsai/rapids-metadata and fetch it during docs builds