fix readme

Author: dakk

README.md

@@ -57,7 +57,7 @@ GWeatherRouting is an opensource sailing route calculator written in python and:
    - eccodes
 
 Note: if you are using a `virtualenv` you need to make symbolic links from the UI libraries to your `venv` folder (this is not needed using system interpreter outside venv).```
-3. install the required python modules with `pip install -r requirements.txt`
+3. install the required python modules with ```pip install -r requirements.txt```
 4. Then checkout the repository and run: ```python setup.py install```
 5. Start the software running: ```gweatherrouting```