minor: add comments about WESHER_E2E_TESTS envvar

[skip ci]

tests/entrypoint.sh

@@ -6,6 +6,7 @@ mkdir -p /dev/net
 mknod /dev/net/tun c 10 200
 
 wireguard-go wgoverlay
+# this disables kernel-mode interface creation; see wireguard.go:createWgInterface()
 export WESHER_E2E_TESTS=1
 
 /app/wesher --log-level debug --cluster-key 'ILICZ3yBMCGAWNIq5Pn0bewBVimW3Q2yRVJ/Be+b1Uc=' "$@"

wireguard.go

@@ -137,6 +137,7 @@ func (wg *wgState) nodesToPeerConfigs(nodes []node) ([]wgtypes.PeerConfig, error
 func (wg *wgState) createWgInterface() error {
 	if _, err := wg.client.Device(wg.iface); err == nil {
 		// device already exists, but we are running e2e tests, so we're using the user-mode implementation
+		// see tests/entrypoint.sh
 		if _, e2e := os.LookupEnv("WESHER_E2E_TESTS"); e2e {
 			return nil
 		}