Update known-issues.md

Author: dpolivaev

src/docs/user-documentation/known-issues.md

@@ -1,3 +1,11 @@
 <!-- toc -->
 
-To be continued
+Freeplane is an actively maintained open-source project. Some limitations are known but cannot be resolved easily due to technical or external constraints.
+
+You can find such issues collected under the following labels on GitHub:
+
+👉 [All “can’t do”, “not our bug”, and “wontfix” issues](https://github.com/freeplane/freeplane/issues?q=label%3A%22can%27t%20do%22%20OR%20label%3A%22not%20our%20bug%22%20OR%20label%3Awontfix)
+
+We maintain these labels to be transparent about problems that are currently out of scope for fixing.
+
+(To be continued)