add Known problems

Author: BaseMax

README.md

@@ -31,3 +31,17 @@ $ heroku builds:cancel -a basemaxrubytest
 $ heroku config:set -a basemaxrubytest DB_HOST=xxx DB_PORT=3306 DB_USERNAME=license_service DB_PASSWORD=xxx
 $ heroku restart -a basemaxrubytest
 ```
+
+#### Known problems
+
+- `An automatic deployment for basemaxrubytest failed. The build failed with the message Your account has reached its concurrent builds limit.`
+
+List of all builds:
+```
+heroku builds -a basemaxrubytest
+```
+
+Stop and kill last running process:
+```
+heroku builds:cancel -a basemaxrubytest
+```