Document build flags that reduce binary size

> Using the -ldflags=-w flags to remove the debug symbols cuts the size of the binary in half too, seems strange that AWS isn't recommending this as well.

With any non-default build flags, there may be some tradeoff to understand and incorporate into any documentation. Dropping the debug symbols does seem risk free though.

_Originally posted by @bmoffatt in https://github.com/aws/aws-lambda-go/issues/493#issuecomment-1500939310_

There's also `-tags lambda.norpc` that could be documented.