A few minor changes regarding documentation, testing, and devops.
- Add section on how to estimate size on disk.
- When mentioning the SDAPI source code, add links both to the Azure repo (active development) and the public version in OSDU.
- paal; Set projection system, source name, and source description in one of the test files. As requested by a user. Note that these are currently not exposed in the api (because yagni) but might easily be added.
- Update the xenial build rules. Yes I know Ubuntu Xenial isn't very relevant any longer.