Edited gitignore and README to make everything work proprely with virtualenv

.gitignore

@@ -1,3 +1,5 @@
 db.sqlite3
 *.pyc
 *__pycache__*
+.DS_Store
+env_sith

README.md

@@ -5,7 +5,10 @@ To start working on the project, just run the following commands:
 
     git clone https://ae-dev.utbm.fr/ae/Sith.git
     cd Sith
-    python3 manage.py migrate
+    virtualenv --clear --python=python3 env_sith
+    source env_sith/bin/activate
+    pip install -r requirements.txt
+    ./manage.py migrate
 
 To load some initial data in the core:
 

requirements.txt

@@ -0,0 +1 @@
+django