Update debugging.rst (#5234)

* Update debugging.rst

PLEASE REVIEW
The current link definitely points to the wrong line, where there's nothing remotely resembling a list of DEBUG_ESP_* definitions. There's not an actual "full list" in the whole boards.txt really, but this is the closest thing that can be found in that file.
Some additional explanation is needed though, unless there is an actual list somewhere else.

* Update debugging.rst

requested change

Author: teo1978

Diff for: doc/Troubleshooting/debugging.rst

@@ -74,7 +74,7 @@ Debug Level
 All defines for the different levels starts with ``DEBUG_ESP_``
 
 a full list can be found here in the
-`boards.txt <https://github.com/esp8266/Arduino/blob/master/boards.txt#L180>`__
+`boards.txt <https://github.com/esp8266/Arduino/blob/master/tools/boards.txt.py#L1045-L1047>`__
 
 Example for own debug messages
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^