Add note about Network Manager

README.md

@@ -128,6 +128,10 @@ If you want to perform these steps by hand, you will need to import the user cer
 Set-VpnConnectionIPsecConfiguration -ConnectionName "Algo" -AuthenticationTransformConstants SHA256128 -CipherTransformConstants AES256 -EncryptionMethod AES256 -IntegrityCheckMethod SHA256 -DHGroup Group14 -PfsGroup none
 ```
 
+### Linux Network Manager Clients (e.g., Ubuntu, Debian, or Fedora Desktop)
+
+Network Manager does not support AES-GCM. In order to support Linux Desktop clients, please choose the "compatible" cryptography and use at least Network Manager 1.4.1. See [Issue #263](https://github.com/trailofbits/algo/issues/263) for more information.
+
 ### Linux strongSwan Clients (e.g., OpenWRT, Ubuntu Server, etc.)
 
 Install strongSwan, then copy the included ipsec_user.conf, ipsec_user.secrets, user.crt (user certificate), and user.key (private key) files to your client device. These will require customization based on your exact use case. These files were originally generated with a point-to-point OpenWRT-based VPN in mind.