chore: add note about external source files not being watched

Author: pawamoy

docs/setup/extensions/mkdocstrings.md

@@ -76,3 +76,18 @@ The complete list of options can be found here:
 
   [mkdocstrings documentation]: https://mkdocstrings.github.io/usage/
   [mkdocstrings Python handler documentation]: https://mkdocstrings.github.io/python/usage/
+
+!!! warning "Watching source files"
+
+    While it is possible to configure search paths that are external to the
+    docs project (outside of the parent directory containing the
+    `zensical.toml` file) in the `paths` option of the Python handler, these
+    external paths will not be watched for change, meaning that modifying
+    files within them will not trigger a rebuild and reload. The reason is that
+    the file agent will refuse to watch files that are outside the project folder
+    for security reasons. We are working on lifting this limitation. You can
+    follow progress on these backlog items:
+
+    - [Proposal: Configuration](https://github.com/zensical/backlog/issues/47)
+    - [Allow use of `..` in `docs_dir` and `site_dir`](https://github.com/zensical/backlog/issues/56)
+    - [Symbolic links pointing outside of `docs_dir`](https://github.com/zensical/backlog/issues/55)