docs: Explain how to turn clang-format of for some blocks of code

CONTRIBUTING.md

@@ -98,6 +98,13 @@ and the `pre-push` hook will be skipped.
 
 *Note:* We provide a config file that describes our coding style for clang. But due to a mistake on their side it might happen that you can get a different result that what we expect. See [here](https://github.com/profanity-im/profanity/pull/1774) and [here](https://github.com/profanity-im/profanity/pull/1828) for details. We will try to always run latest clang-format.
 
+In cases where you want to disable automatic formatting for a specific block of code (e.g. a complex lookup table), you can use the following comments:
+```c
+/* clang-format off */
+// your code
+/* clang-format on */
+```
+
 ## Finding mistakes
 Test your changes with the following tools to find mistakes.