Update README with instructions for local setup and Stripe integration

Added an extensive guide to the README outlining the process for setting up a local environment including a `.env.local` file for storing sensitive information safely. Also included are steps on how to integrate with Stripe and set up the related environment variables.

apps/web/README.md

@@ -1,3 +1,33 @@
 # Your Application
 
 Write here everything about your application.
+
+## Setup
+
+For working locally, please add a file named `.env.local` where we can place our environment variables. This file is not committed to Git, therefore it is safe to store sensitive information in it.
+
+After starting Supabase, copy the service role key from the Supabase project settings and add it to the `.env.local` file.
+
+```
+SUPABASE_SERVICE_ROLE_KEY=your-service-role-key
+```
+
+## Stripe
+
+For the Stripe integration, first we need to start the Stripe CLI:
+
+```
+pnpm run stripe:listen
+```
+
+Then, update the `.env.local` file with the following variables:
+
+```
+STRIPE_WEBHOOK_SECRET=
+STRIPE_SECRET_KEY=
+NEXT_PUBLIC_STRIPE_PUBLISHABLE_KEY=
+```
+
+### Supabase
+
+Please follow the instructions in the [Supabase README](../supabase/README.md) to setup your Supabase project.