Add README

+## Building
+
+# Python Version
+
+    ~$ python3 --version
+    Python 3.8.2
+
+Python 가상환경 사용을 권장합니다.
+
+# pip, django
+
+    ~$ python3 -m pip install --upgrade pip
+    ~$ pip install django~=3.1.2
+    ...
+    Successfully installed asgiref-3.2.10 django-3.1.2 pytz-2020.1 sqlparse-0.3.1
+    
+# Database
+
+    ~/smartdoorlock-backend$ python manage.py migrate
+    ~/smartdoorlock-backend$ python manage.py makemigrations
+    
+# Run Server
+
+    ~/smartdoorlock-backend$ python manage.py runserver
+    
+http://127.0.0.1:8000/ 로 접속
+    
+