tools/compile_test_one_board: update documentation README

Provide some notes on how to perform basic checks on the script using tox

dist/tools/compile_and_test_for_board/README.md

@@ -20,6 +20,20 @@ They can be checked with:
     find results/ -name '*.failed'
     find results/ -name 'test.success'
 
+Script checks
+-------------
+
+Use [tox](https://tox.readthedocs.io/en/latest/) to run basic checks on the
+script:
+
+    $ tox
+
+This runs doctest (via pytest), pylint and flake8 checks in a row.
+Use `-e` to run each check independently:
+
+    $ tox -e test
+    $ tox -e lint
+    $ tox -e flake8
 
 Implementation TODO
 -------------------
@@ -31,6 +45,6 @@ simply adapt to be used from within RIOT.
 * Provide a RIOT/Makefile integration
 * Save output files into `${BUILD_DIR}/output/compile_and_test` directory by
   default
-* tox file to run `doctests/pylint/flake8`. Add tests.
+* Add tests.
 * Implement the `board_is_supported`/`board_has_enough_memory`/`has_tests` to
   make targets instead of fiddling to get the value