* Add cross-build docs Note that C cross compiler is required for building Gitea with `TAGS`. * Apply suggestion from @mrsdizzie Co-Authored-By: mrsdizzie <[email protected]> * Apply suggestion from @guillep2k Co-Authored-By: guillep2k <[email protected]> Co-authored-by: Lunny Xiao <[email protected]> Co-authored-by: mrsdizzie <[email protected]> Co-authored-by: guillep2k <[email protected]> Co-authored-by: John Olheiser <[email protected]>