doc: cmake: prepend build to functional/test_runner.py

README.md

@@ -53,7 +53,8 @@ and extending unit tests can be found in [/src/test/README.md](/src/test/README.
 
 There are also [regression and integration tests](/test), written
 in Python.
-These tests can be run (if the [test dependencies](/test) are installed) with: `test/functional/test_runner.py`
+These tests can be run (if the [test dependencies](/test) are installed) with: `build/test/functional/test_runner.py`.
+Do not run the (identical) program `test/functional/test_runner.py` (without the build directory).
 
 The CI (Continuous Integration) systems make sure that every pull request is built for Windows, Linux, and macOS,
 and that unit/sanity tests are run automatically.

test/functional/README.md

@@ -10,7 +10,7 @@ that file and modify to fit your needs.
 
 #### Coverage
 
-Running `test/functional/test_runner.py` with the `--coverage` argument tracks which RPCs are
+Running `build/test/functional/test_runner.py` with the `--coverage` argument tracks which RPCs are
 called by the tests and prints a report of uncovered RPCs in the summary. This
 can be used (along with the `--extended` argument) to find out which RPCs we
 don't have test cases for.