Bring back normalization and explain submodules in README

Author: mielvds

.github/workflows/main.yaml

@@ -67,6 +67,7 @@ jobs:
       run: |
         python tests/runtests.py ./specifications/json-ld-api/tests -l ${{ matrix.loader }}
         python tests/runtests.py ./specifications/json-ld-framing/tests -l ${{ matrix.loader }}
+        python tests/runtests.py ./specifications/normalization/tests -l ${{ matrix.loader }}
       env:
         LOADER: ${{ matrix.loader }}
   #coverage:

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "specifications/json-ld-framing"]
 	path = specifications/json-ld-framing
 	url = https://github.com/w3c/json-ld-framing.git
+[submodule "specifications/normalization"]
+	path = specifications/normalization
+	url = https://github.com/json-ld/normalization.git

README.rst

@@ -190,15 +190,33 @@ Tests
 This library includes a sample testing utility which may be used to verify
 that changes to the processor maintain the correct output.
 
-To run the sample tests you will need to get the test suite files by cloning
+To run the sample tests you will need to get the test suite files, which by default, are stored in the `specifications/` folder.
+The test suites can be obtained by either using git submodules or by cloning them manually.
+
+## Using git submodules
+
+The test suites are included as git submodules to ensure versions are in sync.  When cloning the repository, use the ``--recurse-submodules`` flag to
+automatically clone the submodules.
+If you have cloned the repository without the submodules, you can initialize them with the following commands:
+
+.. code-block:: bash
+
+    git submodule init
+    git submodule update
+
+## Cloning manually
+
+You can also avoid using git submodules by manually cloning
 the ``json-ld-api``, ``json-ld-framing``, and ``normalization`` repositories
 hosted on GitHub:
 
 - https://github.com/w3c/json-ld-api
 - https://github.com/w3c/json-ld-framing
 - https://github.com/json-ld/normalization
 
-If the suites repositories are available as sibling directories of the PyLD
+## Running the tests
+
+If the suites repositories are available in the `specifications/` folder of the PyLD
 source directory, then all the tests can be run with the following:
 
 .. code-block:: bash