docs: add HTTP link for Mesa downloads
docs: add HTTP link for Mesa downloads

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92628
Reviewed-by: Jose Fonseca <61b5a29db2c0650f7c8510f93eece059c1b09320@vmware.com>
Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler