Fix installation guide

doc/source/installation.rst

@@ -16,7 +16,7 @@ You can then install storm and pycarl independently.
 
 .. topic:: Virtual Environments
 
-	Virtual environments create isolated environments for your projects. This helps to keep your system clean, work with different versions of packages and different version of python. While it is not required, we recommend the use of
+	Virtual environments create isolated environments for your projects. This helps to keep your system clean, work with different versions of packages and different versions of python. While it is not required, we recommend the use of
 	such virtual environments. To get you started, we recommend `this guide <http://docs.python-guide.org/en/latest/dev/virtualenvs/>`_ or `this primer <https://realpython.com/blog/python/python-virtual-environments-a-primer>`_.
 
 
@@ -40,9 +40,9 @@ or::
 .. topic:: Specifying which storm library to use
 
 	If you have multiple versions of storm or cmake is not able to find your storm version, 
-	you can specify the `--storm-DIR YOUR-PATH-TO-STORM` flag in the build_ext step::
+	you can specify the `--storm-dir YOUR-PATH-TO-STORM` flag in the build_ext step::
 	
-	$ python3 setup.py build_ext --storm-DIR YOUR-PATH-TO-STORM develop
+	$ python3 setup.py build_ext --storm-dir YOUR-PATH-TO-STORM develop
 	
 After building, you can run the test files by::