doc(build): improve practial pytest marker help

Author: ankostis

setup.cfg

@@ -7,7 +7,7 @@ universal = 1
 [tool:pytest]
 # See http://doc.pytest.org/en/latest/mark.html#mark
 markers =
-    slow: marks tests as slow, select them with `-m slow` or `-m 'not slow'`
+    slow: slow-running tests, run them: with: -m slow OR -m 'slow and not slow'
 
 # TODO: enable doctests in README.
 addopts         = graphtik/ test/ docs/source/ README.rst
@@ -23,4 +23,3 @@ addopts         = graphtik/ test/ docs/source/ README.rst
     --doctest-glob=*.rst
     --cov-fail-under=80
 doctest_optionflags = NORMALIZE_WHITESPACE ELLIPSIS
-