chore: add .dev.vars.example and update README with environment setup instructions

Author: foxlau

.dev.vars.example

@@ -0,0 +1,12 @@
+ENVIRONMENT = "development" # development | production
+
+APP_URL = "http://localhost:5173"
+SESSION_SECRET = "3ebc25b381e87193f29ffea6b6d380dd"
+
+GITHUB_CLIENT_ID = "..."
+GITHUB_CLIENT_SECRET = "..."
+
+GOOGLE_CLIENT_ID = "..."
+GOOGLE_CLIENT_SECRET = "..."
+
+RESEND_API_KEY = "..."

README.md

@@ -26,7 +26,7 @@ An introductory starter kit for building applications with React Router v7 (Remi
 
 ## Demo
 
-Here’s a preview of the app:
+Here's a preview of the app:
 
 <div style="display: flex;">
   <img src="./.assets/login.png" width="45%" />
@@ -60,6 +60,14 @@ npm install
 
 ### Development
 
+First, copy the .dev.vars.example file and rename it to .dev.vars:
+
+```bash
+cp .dev.vars.example .dev.vars
+```
+
+Update the environment variables in the .dev.vars file according to your needs. These variables will be used by Wrangler during local development.
+
 Run an initial database migration:
 
 ```bash