Debugging instructions incorrect

[pettermahlen]

When I tried to follow the debugging instructions in the README, they didn't work - there was an error about not being able to find ```
bazel-out/darwin_arm64-opt-exec-2B5CBBC6/bin/external/io_bazel_rules_kotlin/src/main/kotlin/build.runfiles/external/com_github_jetbrains_kotlin/lib/jvm-abi-gen.jar

This file isn't mentioned in the flagfile as described in step 6 of the current instructions. 

I was able to run the command I wanted to debug with the debug port by cd:ing into the execRoot (`bazel-MYPROJECT`), which also meant there was no need to edit the flagfile. I'm not sure if that's the correct solution, but I'll create a PR to update the instructions accordingly.