Add warning about 3rd-party antivirus

Author: barrykn

README.md

@@ -62,12 +62,14 @@ Currently not supported by this patcher, but future support may be possible:
 - As mentioned at the top of this README, 2008 Mac Pro owners should use StarPlayrX's Big Mac patcher instead of this patcher.
 
 ## Other important information to know before upgrading or installing
-I *strongly recommend* that you create, and hold onto, an [installer USB for an older version of macOS](https://support.apple.com/en-us/HT201372), perhaps one that is supported on your Mac (so that it can run without the use of a patcher). Or, at the absolute minimum, *practice* booting into Internet Recovery (boot while holding down Command-Option-R) so that you know it actually works. Once it boots, try starting Safari and (as a test) see if it can visit GitHub.com. If not, then it may have booted into OS X Lion, which is also old enough that attempting to install it through Internet Recovery will fail. (Internet Recovery tends to be especially likely to boot into Lion if you have only 4GB of RAM. Also, if you have upgraded to an 802.11ac WiFi card, Internet Recovery will fail completely unless you plug into Ethernet. In addition, with the possible exception of flashed 2009 Mac Pros, Internet Recovery is not available on any Mac models prior to 2010.)
+I *strongly recommend* that you create, and hold onto, an [installer USB for an older version of macOS](https://support.apple.com/en-us/HT201372), ideally one that is supported on your Mac (so that it can run without the use of a patcher). Or, at the absolute minimum, *practice* booting into Internet Recovery (boot while holding down Command-Option-R) so that you know it actually works. Once it boots, try starting Safari and (as a test) see if it can visit GitHub.com. If not, then it may have booted into OS X Lion, which is also old enough that attempting to install it through Internet Recovery will fail. (Internet Recovery tends to be especially likely to boot into Lion if you have only 4GB of RAM. Also, if you have upgraded to an 802.11ac WiFi card, Internet Recovery will fail completely unless you plug into Ethernet. In addition, with the possible exception of flashed 2009 Mac Pros, Internet Recovery is not available on any Mac models prior to 2010.)
 
 In any case, if you are unable to start Internet Recovery, or it has a version of Safari too old to visit GitHub.com, then it is *vital* that you create an installer USB for an older macOS version and hold onto it in case of emergency.
 
 Once you create the patched installer USB for Big Sur, hold onto it as well. If you ever reset your Mac's NVRAM, then you will need to use the patched installer USB to repeat step 9 of the installation instructions.
 
+If you have installed any 3rd-party antivirus program or security suite, make sure to uninstall it before installing Big Sur (or do a fresh installation instead of an upgrade). It is not sufficient to turn the antivirus program off -- it must be uninstalled. If you do not uninstall it, you may have no Internet connection after Big Sur is installed, and the Wi-Fi patch may fail to work.
+
 On a Mac without a Metal GPU, several programs, including Maps and Photos, will not work. Perhaps there may be patches in the future to provide partial fixes, but upgrading to a Metal GPU is the only actual solution.
 
 FileVault has been buggy throughout the entire Big Sur development cycle. For maximum stability, disable FileVault before upgrading to Big Sur. Once you upgrade to Big Sur, bugs may make it impossible to disable FileVault and may make it impossible to unlock your FileVault volumes when applying updates or booting from the installer USB. (Not to mention, FileVault bugs may also make it impossible to open Terminal on the installer USB.) The best way out of this conundrum is probably to back up the entire Big Sur installation using Time Machine (Time Machine encryption, unlike FileVault, appears to be stable), erase and reinstall Big Sur, and use the Setup Assistant to restore the Time Machine backup.