docs(std.base64): Add references to RFC 4648
There are multiple implementations of Base64, but `std.base64` appears
to be based on RFC 4648, so we clarify that it is based on RFC 4648.
f062ec2a1aShun Sakai committed on 3/24/2025, 2:31:58 PM· committed by Alex Rønne Petersenparenta7cfc23