docs: Add README badge for acceptance tests (#1104)

Author: barbeau

README.md

@@ -1,4 +1,4 @@
-# gtfs-validator [![Test Package Document](https://github.com/MobilityData/gtfs-validator/workflows/Test%20Package%20Document/badge.svg)](https://github.com/MobilityData/gtfs-validator/actions?query=workflow%3A%22Test+Package+Document%22) ![End to end](https://github.com/MobilityData/gtfs-validator/workflows/End%20to%20end/badge.svg) ![End to end big](https://github.com/MobilityData/gtfs-validator/workflows/End%20to%20end%20big/badge.svg) ![End to end 100](https://github.com/MobilityData/gtfs-validator/workflows/End%20to%20end%20100/badge.svg) ![Docker image](https://github.com/MobilityData/gtfs-validator/actions/workflows/docker.yml/badge.svg) [![Join the gtfs-validator chat](https://badgen.net/badge/slack/%20/green?icon=slack)](https://bit.ly/mobilitydata-slack)
+# gtfs-validator [![Test Package Document](https://github.com/MobilityData/gtfs-validator/workflows/Test%20Package%20Document/badge.svg)](https://github.com/MobilityData/gtfs-validator/actions?query=workflow%3A%22Test+Package+Document%22) ![End to end](https://github.com/MobilityData/gtfs-validator/workflows/End%20to%20end/badge.svg) ![End to end big](https://github.com/MobilityData/gtfs-validator/workflows/End%20to%20end%20big/badge.svg) ![End to end 100](https://github.com/MobilityData/gtfs-validator/workflows/End%20to%20end%20100/badge.svg) [![Rule acceptance tests](https://github.com/MobilityData/gtfs-validator/actions/workflows/acceptance_test.yml/badge.svg)](https://github.com/MobilityData/gtfs-validator/actions/workflows/acceptance_test.yml) ![Docker image](https://github.com/MobilityData/gtfs-validator/actions/workflows/docker.yml/badge.svg) [![Join the gtfs-validator chat](https://badgen.net/badge/slack/%20/green?icon=slack)](https://bit.ly/mobilitydata-slack)
 
 A GTFS Schedule (static) [General Transit Feed Specification (GTFS)](https://gtfs.mobilitydata.org/spec/gtfs-schedule) feed validator