docs: rust: clarify panicking

Link: https://lore.kernel.org/lkml/CAKwvOdmXNAm+TcypR0dCayp9bJ7RFcgLx5sB8_2MfzO31T3PJg@mail.gmail.com/
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Documentation/rust/docs.rst

@@ -87,7 +87,9 @@ This example showcases a few ``rustdoc`` features and some common conventions
   safe under a ``Safety`` section.
 
 * While not shown here, if a function may panic, the conditions under which
-  that happens must be described under a ``Panics`` section.
+  that happens must be described under a ``Panics`` section. Please note that
+  panicking should be very rare and used only with a good reason. In almost
+  all cases, you should use a fallible approach, returning a `Result`.
 
 * If providing examples of usage would help readers, they must be written in
   a section called ``Examples``.