Check for python 3.

backend/README.md

@@ -7,7 +7,7 @@ part.
 
 ## Linux & Ubuntu guide
 
-1 Install python and virtualenv 
+1 Install python and virtualenv. We recommend to use python 3, but probably python 2 solution will work too.  
 ```
 apt install python3.6
 pip3 install virtualenv

backend/start.sh

@@ -1,8 +1,14 @@
 #!/usr/bin/env bash
-virtualenv -p python3 env3
-source env3/bin/activate
-pip install -r requirements.txt
-python server.py
+if command -v python3 &>/dev/null; then
 
-echo "Server started"
-echo "Go to http://localhost:8200"
+    virtualenv -p python3 env3
+    source env3/bin/activate
+    pip install -r requirements.txt
+    python server.py
+
+    echo "Server started"
+    echo "Go to http://localhost:8200"
+
+else
+    echo "Python 3 is not installed. Or you can try patch this script to Python 2 (change python3 to python2)"
+fi