revolt-bugs.md: add a note

notepad/revolt-bugs.md

@@ -18,6 +18,12 @@
 - Using non-escaped (by a backslash) `<` followed by some text, `>`, and nothing else in a quote results in reduction of space between the visual quote block and the quote.
 - When replying to messages, a single message or multiple messages being replied to are parsed as markdown, but as if all line breaks (newlines) have been removed, which creates a mix-up.
 
+## Notes
+
+- KaTeX code which starts with `%` (a comment) is not rendered and can be used to hide text.
+
+  Example: `It's a regular message$%, unless you copy it$.`
+
 ## Conclusions
 
 - Markdown mode should be optional.