Merge pull request #358 from tracim/fix/348/venv_python_version

README.md

 
 Create a python virtual environment:
 
-    virtualenv -p /usr/bin/python3.4 tg2env
+    virtualenv -p /usr/bin/python3 tg2env
 
 Activate it in your terminal session (**all tracim command execution must be executed under this virtual environment**):