add readme

email-to-webhook/README.md

@@ -0,0 +1,14 @@
+# email_to_webhook
+
+put it in `/root/.forward`:
+
+```
+|"/usr/bin/envdir /etc/environment.d /usr/local/bin/email_to_webhook"
+```
+
+Then:
+
+```
+mkdir -p /etc/environment.d
+echo "https://hooks.slack.com/services/blah/blah/secretblah" > /etc/environment.d/SLACK_WEBHOOK_URL
+```