📚 Documentation: README points to the wrong twitter account

### 💭 Description

Appwrite moved from @appwrite_io to @appwrite on twitter, but the README still points to the old account.

### 👀 Have you spent some time to check if this issue has been raised before?

- [x] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/appwrite/appwrite/blob/HEAD/CODE_OF_CONDUCT.md)