docs: add signup command to README.md with link to Storyblok signup page

Author: alvarosabu

src/README.md

@@ -31,6 +31,7 @@ npm install storyblok@4.0.0-beta.<version>
 | [`migrations run`](./commands/migrations/run/README.md) | ✅ | Replaces previous run-migrations |
 | [`migrations rollback`](./commands/migrations/rollback/README.md) | ✅ | Replaces previous rollback-migrations |
 | [`types generate`](./commands/types/generate/README.md) | ✅ | Replaces previous generate-typescript-typedefs |
+| [`signup`](./commands/signup/README.md) | ✅ | Opens the Storyblok signup page in your browser |
 | `sync` | ⚠️ | Pending new API endpoint implementation for improved performance and reliability (Check below for more details) |
 | `datasources pull` | 📝 | |
 | `datasources push` | 📝 | |