doc: fix/add link to Android info
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
doc, build
We have two notes in API docs about Android support: the first has no links, the second links to the table of supported OSs where Android is not mentioned which may be confusing.
This PR makes both notes link to dedicated Android part of BUILDING.md.