Document CALLBACK_MSG_MODULE_IMPORTED.
Document CALLBACK_MSG_MODULE_IMPORTED.

Looks like this was never documented in the recent changes.

tanium/yara,wxsBSD/yara,mgoffin/yara,bmagistro/yara,rednaga/yara,cblichmann/yara,tanium/yara,msuvajac/yara,pombredanne/yara,plusvic/yara,wxsBSD/yara,cblichmann/yara,cblichmann/yara,MeteorAdminz/yara,rednaga/yara,wxsBSD/yara,hillu/yara,jpypi/yara,pombredanne/yara,Security513/yara,jpypi/yara,plusvic/yara,wxsBSD/yara,cblichmann/yara,plusvic/yara,MeteorAdminz/yara,hillu/yara,msuvajac/yara,MeteorAdminz/yara,rednaga/yara,pombredanne/yara,VirusTotal/yara,plusvic/yara,bmagistro/yara,mgoffin/yara,VirusTotal/yara,cblichmann/yara,VirusTotal/yara,hillu/yara,bmagistro/yara,VirusTotal/yara,hillu/yara,kallanreed/yara,plusvic/yara,Security513/yara,jpypi/yara,pombredanne/yara,Security513/yara,wxsBSD/yara,pombredanne/yara,tanium/yara,hillu/yara,msuvajac/yara,mgoffin/yara,mgoffin/yara,kallanreed/yara,VirusTotal/yara,kallanreed/yara