Update create-buckets.mdx

Bucket names can't start with a number.

Author: cf-scott

src/content/docs/r2/buckets/create-buckets.mdx

@@ -25,7 +25,7 @@ wrangler r2 bucket create your-bucket-name
 
 :::note
 
-Bucket names can only contain lowercase letters (a-z), numbers (0-9), and hyphens (-).
+Bucket names must begin with a letter, and can only contain lowercase letters (a-z), numbers (0-9), and hyphens (-).
 
 The placeholder text is only for the example.