Update readme.md - missing dependency added

readme.md

 # SMart SCHeduling
 
 ## Required software (on ubuntu's OS family):
-  - `sudo apt-get install libpq-dev python-dev postgresql postgresql-contrib python virtualenv python-virtualenv`
+  - `sudo apt-get install libpq-dev python-dev postgresql postgresql-contrib python virtualenv python-virtualenv gcc`
 
 ## Postgres installation
   - If you don't have postgres installed, complete step seven from [https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-django-with-postgres-nginx-and-gunicorn](https://www.digitalocean.com/community/tutorials/how-to-install-and-configure-django-with-postgres-nginx-and-gunicorn) (remember to save all the credentials, they will be necessary to run the application).