Add some basic docs to help with debugging

Signed-off-by: falkTX <falktx@falktx.com>

carla

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-Subproject commit b1ecb33a5ec8d24a98a93ed038713a6da6cc9701
+Subproject commit 74a1ae82c90db85f20550ddcdc8a927b8fb7e414

doc/DEBUGGING.md

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+# Building
+
+This document describes a few possible ideas to help debug Cardinal issues.  
+It requires a recent build of Carla, that being >= v2.4.2, in order to work correctly.
+
+Cardinal must be built from source with `make DEBUG=true` for any useful information to be available with these steps.
+
+## Plugin scanning
+
+We can use command-line carla-discovery tools together with valgrind to quickly check for memory errors and leaks.  
+By default carla-discovery will do 1 audio processing/run block for testing, which is handy for us here.
+
+```
+valgrind --leak-check=full --track-origins=yes --suppressions=./dpf/utils/valgrind-dpf.supp \
+/usr/lib/carla/carla-discovery-native vst2 ./bin/CardinalFX.vst/CardinalFX.so
+```
+
+## Plugin usage
+
+For regular plugin usage we can use carla-bridge tools, set as dummy mode so audio does not need to run in realtime.  
+We set dummy=30 in order to only trigger audio processing every 30s,
+otherwise the audio thread would take all of valgrind's time and it would appear as if it was halted.
+
+It is recommended to remove all modules from the Rack except for the strictly necessary ones for debug.
+
+```
+env CARLA_BRIDGE_DUMMY=1 \
+valgrind --leak-check=full --track-origins=yes --suppressions=./dpf/utils/valgrind-dpf.supp \
+/usr/lib/carla/carla-bridge-native vst2 ./bin/CardinalFX.vst/CardinalFX.so ""
+```