doc: document uv_fs_realpath caveats
doc: document uv_fs_realpath caveats

Fixes: https://github.com/libuv/libuv/issues/1017
PR-URL: https://github.com/libuv/libuv/pull/1026
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>
Reviewed-By: Imran Iqbal <d6d3ccaa384a65532061e26836842adc48d43df4@imraniqbal.org>

unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso,unknownbrackets/maxcso