Update services/postprocessing/README.md

Co-authored-by: Martin <github@diemattels.at>

services/postprocessing/README.md

@@ -31,7 +31,7 @@ To enable virus scanning as a postprocessing step after uploading a file, the en
 Though this is for development purposes only and NOT RECOMMENDED on production systems, setting the environment variable `POSTPROCESSING_DELAY` to a duration not equal to zero will add a delay step with the configured amount of time. ocis will continue postprocessing the file after the configured delay. Use the enviroment variable `POSTPROCESSING_STEPS` and the keyword `delay` if you have multiple postprocessing steps and want to define their order. If `POSTPROCESSING_DELAY` is set but `delay` is not contained in `POSTPROCESSING_STEPS` it will be added as last postprocessing step.
 
 ### Custom Postprocessing Steps
-Using the envvar `POSTPROCESSING_STEPS` custom postprocessing steps can be added. Any word can be used as step name but be careful not to clash with exising steps `virusscan` and `delay`.
+By using the envvar `POSTPROCESSING_STEPS`, custom postprocessing steps can be added. Any word can be used as step name but be careful not to conflict with exising keywords like `virusscan` and `delay`. In addition, if a keyword is misspelled or the corresponding service does either not exist or does not follow the necessary event communication, the postprocessing service will wait forever getting the required response to proceed and does not continue any other processing.
 
 #### Prerequisites
 For using custom postprocessing steps you need a custom service listening to the configured event system (see `General Prerequisites`)