Correct the description of the default state of test module compilation.
are not shipped. All other modules are bundled as pre-compiled
``pyc`` files.
- In-memory file system (MEMFS) is not persistent and limited.
-- Test modules are disabled by default. Use ``--enable-test-modules`` build
- test modules like ``_testcapi``.
+- Test modules are built by default. Use ``--disable-test-modules`` to disable
+ building test modules like ``_testcapi``.
## Detecting Emscripten builds