added a bit of documentation on how to run tests

README.rst

@@ -293,6 +293,32 @@ To install DSMR Parser:
 
     $ pip install dsmr-parser
 
+Development
+-----------
+
+Create a virtualenv and activate it followed by the installation of the dsmr-parser:
+```
+python3 -m venv venv
+source venv/bin/activate
+pip install -e .
+```
+
+Install tox and run it:
+```
+pip install tox
+tox
+```
+
+You should see that the tests have succeeded:
+```
+======================================================================================================== 59 passed in 0.91s ========================================================================================================
+py: commands[1]> pylama dsmr_parser test
+  py: OK (11.55=setup[9.73]+cmd[1.29,0.53] seconds)
+  congratulations :) (11.69 seconds)
+```
+
+Now you can make changes by editing the code and rerunning tox to verify your changes.
+
 Known issues
 ------------