Add note about not being able to use this module with modules not
implemented in Python.
diff --git a/Doc/lib/libpyclbr.tex b/Doc/lib/libpyclbr.tex
index aba83f8..8e89fcf 100644
--- a/Doc/lib/libpyclbr.tex
+++ b/Doc/lib/libpyclbr.tex
@@ -12,7 +12,9 @@
provided is sufficient to implement a traditional three-pane class
browser. The information is extracted from the source code rather
than from an imported module, so this module is safe to use with
-untrusted source code.
+untrusted source code. This restriction makes it impossible to use
+this module with modules not implemented in Python, including many
+standard and optional extension modules.
\begin{funcdesc}{readmodule}{module\optional{, path}}