doc: document buffer's "Uint" aliases clearly

Fixes: https://github.com/nodejs/node/issues/36751

PR-URL: https://github.com/nodejs/node/pull/36796


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Harshitha K P <harshitha014@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>