add release notes for filesystem fixes

Update doc/manual/rl-next/filesystem-errors.md

Co-authored-by: John Ericson <git@JohnEricson.me>

doc/manual/rl-next/filesystem-errors.md

@@ -0,0 +1,14 @@
+---
+synopsis: wrap filesystem exceptions more correctly
+issues: []
+prs: [11378]
+---
+
+
+With the switch to `std::filesystem` in different places, Nix started to throw `std::filesystem::filesystem_error` in many places instead of its own exceptions.
+
+This lead to no longer generating error traces, for example when listing a non-existing directory, and can also lead to crashes inside the Nix REPL.
+
+This version catches these types of exception correctly and wrap them into Nix's own exeception type.
+
+Author: [**@Mic92**](https://github.com/Mic92)