Created Debugging the Nim compiler (markdown)

Debugging-the-Nim-compiler.md

@@ -0,0 +1,15 @@
+Due to Nimbus sometimes using niche features of the Nim compiler, we might encounter compiler crashes or semantic check errors with no clue how to proceed forward and a lot of difficulty to create a minimal test case.
+
+2 strategies to kickstart an investigation are available. The first one is to compile a Nim compiler with stack traces enabled.
+
+## Nim compiler with stack traces
+
+1. Clone Nim and build `koch` as in the Nim readme.
+2. Create a temporary Nim compiler with stacktraces, for example to debug https://github.com/status-im/nimbus/issues/322, this is the command to reproduce the bug:
+      ```sh
+      ./koch temp c -r -o:build/gascosts ../../Status/nimbus/tests/all_tests.nim # Replace by your own path
+      ```
+
+## Bisecting
+
+You can use git bisect to narrow down the offending commit. Usually only `koch boot -d:release` is needed to rebuild `bin/nim` but sometimes you need to re-bootstrap the `koch` and potentially the `csources`