[NFC] Inclusive Language: change master to main for .chm files

[NFC] As part of using inclusive language within the llvm project,
this patch replaces master with main when referring to `.chm` files.

Reviewed By: teemperor

Differential Revision: https://reviews.llvm.org/D113299

GitOrigin-RevId: c3b15b71ce009b3dff9fb3bd664d087057b8376e
1 file changed