add readme

Readme.md

+# URL Shorter
+This is a very simple URL Shortener written in PHP.
+There is a simple API available at '/api', which gets used by the [Firefox Extension](https://jle.xyz/9ymrw)
+
+## Setup
+```bash
+# Install Dependencies
+composer install
+
+# Copy the .env to .env.local
+cp .env .env.local
+
+# Setup the database connection
+# Then run the database migrations
+php bin/console doctrine:migrations:migrate
+```
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