config/network: add groups for ConnMan and IWD

Author: cinerea0

src/config/network/connman.md

@@ -15,6 +15,8 @@ Finally, enable the `connmand` service.
 
 ## Configuring ConnMan
 
+Users of ConnMan must belong to the `network` group.
+
 ### ConnMan CLI
 
 The `connman` package includes a command line tool,

src/config/network/iwd.md

@@ -15,8 +15,8 @@ as arguments; when run without arguments, it provides an interactive session. To
 list available commands, run `iwctl help`, or run `iwctl` and enter `help` at
 the interactive prompt.
 
-By default, only the root user and those in the `wheel` group have permission to
-operate `iwctl`.
+By default, only the root user and those in the `wheel` or `netdev` groups have
+permission to operate `iwctl`.
 
 ## Configuration