duplicate_pin_override: Debugging tool to permit multiple use pins

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

docs/Config_Reference.md

@@ -1574,6 +1574,22 @@ main printer config file. Wildcards may also be used (eg,
 [include my_other_config.cfg]
 ```
 
+## [duplicate_pin_override]
+
+This tool allows a single micro-controller pin to be defined multiple
+times in a config file without normal error checking. This is intended
+for diagnostic and debugging purposes. This section is not needed
+where Klipper supports using the same pin multiple times, and using
+this override may cause confusing and unexpected results.
+
+```
+[duplicate_pin_override]
+pins:
+#   A comma separated list of pins that may be used multiple times in
+#   a config file without normal error checks. This parameter must be
+#   provided.
+```
+
 # Bed probing hardware
 
 ## [probe]