Set pool size via MAX_POOL_SIZE

Procfile

@@ -1,5 +1,5 @@
 worker:         bundle exec rake jobs:work
 rabbit_workers: bin/rails r lib/rabbit_workers.rb
-web:            bundle exec passenger start -p $PORT -e $RAILS_ENV --max-pool-size 12
+web:            bundle exec passenger start -p $PORT -e $RAILS_ENV --max-pool-size $MAX_POOL_SIZE
 # This will perform a hard refresh on all connected browsers.
 release:        rails r "User.refresh_everyones_ui"

example.env

@@ -16,6 +16,9 @@
 # found in API_HOST. Heroku users will not use the same value.
 # Use a REAL, PUBLIC IP ADDRESS if you are controlling real bots.
 MQTT_HOST=98.76.54.32
+# Set the max pool size for Passenger.
+# Only needed if using Heroku. FarmBot, Inc. uses Heroku. Self hosters do not.
+MAX_POOL_SIZE=2
 # If your server is on a domain (eg=my-own-farmbot.com), put it here.
 # DONT USE `localhost`.
 # DONT USE `127.0.0.1`.