Update README.md and .env.example: correct database type to MongoDB and simplify database setup instructions

Author: austenstone

backend/.env.example

@@ -18,4 +18,4 @@ MONGODB_URI=mongodb://localhost:27017/github-value
 
 # Webhook proxy URL (optional)
 # This is only needed if you don't want to use smee.io
-# WEBHOOK_PROXY_URL=https://5950-2601-589-4885-e850-b1eb-a754-b856-6038.ngrok-free.app
+# WEBHOOK_PROXY_URL=https://5950-2601-589-4885-e850-b1eb-a754-b856-6038.ngrok-free.app

backend/README.md

@@ -9,21 +9,11 @@ npm run dev
 ```
 
 ## Database
-The backend uses a MySQL database to store data.
+The backend uses a MongoDB database to store data.
 
 You can run the docker compose file to start the database. Just shutdown the backend server so you can free up the port.
-
-You can also run it manually:
 ```bash
-docker run -d \
-  --name db \
-  --restart always \
-  -e MYSQL_PASSWORD=octocat \
-  -e MYSQL_DATABASE=value \
-  -p 3306:3306 \
-  -v db:/var/lib/mysql \
-  -v ./db/init.sql:/docker-entrypoint-initdb.d/init.sql \
-  mysql
+docker-compose up -d mongo
 ```
 
 ## API Endpoints