Add account_id to wrangler.toml (#1)

account_id is required when you have more than one account in your
login profile. Add them as optional flags so someone who might use
it don't need to figure out what to do (well, it's pretty trivial
but saving time is always good...)

Signed-off-by: Yongmin Hong <revi@pobox.com>

wrangler.toml

@@ -3,3 +3,5 @@ type = "webpack"
 compatibility_flags = []
 workers_dev = true
 compatibility_date = "2021-10-12"
+# account_id is required if you have multiple accounts within single profile.
+# account_id = ""