fix manual setup instructions

README.md

@@ -240,9 +240,12 @@ Run the app:
 ```commandline
 sh <(curl https://pkgx.sh) +python.org +virtualenv.pypa.io sh
 
-pip install gunicorn
+python -m venv .
 
-source venv/bin/activate
+source bin/activate
+
+# first time
+pip install -r requirements.txt
 
 cp data/webpush.db.empty data/webpush.db