Document how to debug individual test cases in VS Code

This is incredibly helpful because it allows for setting breakpoints,
watches, single-stepping and more.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.vscode/launch.json

@@ -7,6 +7,7 @@
       "name": "Debug Tests",
       "program": "${workspaceRoot}/node_modules/.bin/jest",
       "cwd": "${workspaceRoot}",
+      // to restrict running to a particular test case, add something like "--testNamePattern=/deploy"
       "args": ["--runInBand", "--config", "jest.config.js"],
       "windows": {
         "program": "${workspaceFolder}/node_modules/jest/bin/jest"