Add slack webhook

Sometimes the web log display is SLOW and never updates.

script.sh

@@ -26,6 +26,11 @@ echo To connect to this session copy-n-paste the following into a terminal:
 tmate -S /tmp/tmate.sock display -p '#{tmate_ssh}'
 echo After connecting you can run 'touch /tmp/keepalive' to disable the 15m timeout
 
+if [[ ! -z "$SLACK_WEBHOOK_URL" ]]; then
+  MSG=$(tmate -S /tmp/tmate.sock display -p '#{tmate_ssh}')
+  curl -X POST -H 'Content-type: application/json' --data "{\"text\":\"$MSG\"}" $SLACK_WEBHOOK_URL
+fi
+
 # Wait for connection to close or timeout in 15 min
 timeout=$((15*60))
 while [ -S /tmp/tmate.sock ]; do