added install instructions

INSTALL.md

+
+* install PostgreSQL 8.3+
+
+* make sure you have virtualenv installed:
+http://www.virtualenv.org/en/latest/
+
+* download helios-server
+
+* cd into the helios-server directory
+
+* create a virtualenv:
+
+     virtualenv venv
+
+* activate virtual environment
+
+     source venv/bin/activate
+
+* install requirements
+
+     pip install -r requirements.txt
+
+* reset
+
+     ./reset.sh
+
+* start server
+
+     python manage.py runserver
+