design/40724-register-calling: add design doc
design/40724-register-calling: add design doc

Change-Id: Ib491db5e2523acf6f21b94924339a22d236717bc
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/248178
Reviewed-by: Keith Randall <8c99c3a9284e493be632950b84cd789d08ed3e9d@golang.org>
Reviewed-by: Cherry Zhang <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Martin Möhrmann <9c82b83f348009b39856043bb9ed3ef41e171aeb@google.com>
Reviewed-by: Michael Knyszek <4473450dc5c88f06e1fb787f303d7805ec2aee65@google.com>
Reviewed-by: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>

golang/proposal,golang/proposal