Address @str4d's comments on unit-tests doc. ref #1530

Signed-off-by: Daira Hopwood <daira@jacaranda.org>

doc/unit-tests.md

@@ -10,7 +10,8 @@ There are two scripts for running tests:
 * ``qa/pull-tester/rpc-tests.sh``, to run the RPC tests.
 
 The main test suite uses two different testing frameworks. Tests using the Boost
-framework are under ``src/test/``, and tests using the Google Test/Google Mock
-framework are under ``src/gtest/``. The latter is preferred for new Zcash unit tests.
+framework are under ``src/test/``; tests using the Google Test/Google Mock
+framework are under ``src/gtest/`` and ``src/wallet/gtest/``. The latter framework
+is preferred for new Zcash unit tests.
 
 RPC tests are implemented in Python under the ``qa/rpc-tests/`` directory.