Document PEP 738 in "Platform compatibility tags" specification

[di]

Issue Description

PEP 738 is accepted: https://peps.python.org/pep-0738/

Per python/peps#4250, https://packaging.python.org/en/latest/specifications/platform-compatibility-tags/ should be updated to include PEP 738, as well as any updates/clarifications necessary to implement it.

Code of Conduct

• I am aware that participants in this repository must follow the PSF Code of Conduct.

[mhsmith]

Just adding the word "Android" for searchability.