Add documentation on running unit tests to install verification

docs/source/user/verify_installation.rst

@@ -1,10 +1,32 @@
 Verifying that the installation of Nalu-Wind works
 ==================================================
 
-To verify that the build was successful and that your installation of Nalu-Wind works you can run one of the regression test cases.
+To verify that the build was successful and that your installation of Nalu-Wind works you can run the unit tests and one of the regression test cases.
+
+Unit Tests
+----------
+
+Running
+~~~~~~~
+
+Create a new folder and change into it (the following command creates various files, and this makes it easier to delete them again)
+Then, run the binary :code:`unittestX` contained in your installation of Nalu-Wind.
+
+Expected result
+~~~~~~~~~~~~~~~
+
+At the end of the output a test summary should be printed.
+Ideally, all tests should have passed with possibly a few being skipped and no failures.
+In this case the exit code should be 0.
+
+However, a few failures do not necessarily imply your installation is broken.
+It could be caused by various factors.
+
+Regression Test Case
+--------------------
 
 Preparation
------------
+~~~~~~~~~~~
 
 First download the submodule `reg_tests/mesh`:
 
@@ -13,7 +35,7 @@ First download the submodule `reg_tests/mesh`:
     git submodule update --init reg_tests/mesh/
 
 Running
--------
+~~~~~~~
 
 Change to the directory `reg_tests/test_files/ablNeutralEdge` and run `naluX` on the input there:
 
@@ -23,7 +45,7 @@ Change to the directory `reg_tests/test_files/ablNeutralEdge` and run `naluX` on
     naluX -i ablNeutralEdge.yaml
 
 Expected result
----------------
+~~~~~~~~~~~~~~~
 
 Nalu-Wind will now run (should take a moment).
 It should log nothing or at most a few informational lines and exit cleanly (exit code 0).