x/review/git-codereview: incomplete help documentation for `git codereview`

[gIthuriel]

What version of Go are you using (go version)?

$ go version
go version go1.15 linux/amd64

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/ithuriel/.cache/go-build"
GOENV="/home/ithuriel/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/ithuriel/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/ithuriel/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/ithuriel/go/src/golang.org/x/oauth2/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build639262882=/tmp/go-build -gno-record-gcc-switches"

What did you do?

N/A

What did you expect to see?

Since git codereview mail supports the -nokeycheck option, I would expect to see that documented.

What did you see instead?

As far as I can tell, this option isn't listed anywhere in the documentation. git codereview help doesn't mention it, and the longer documentation doesn't mention it either. I only figured out that the option exists by reading the source code, which isn't ideal.

The longer documentation does say that

The “git codereview mail” command requires an explicit revision argument, but note that since “git codereview mail” is implemented as a “git push”, any commits earlier in the stack are necessarily also mailed.

However, I don't think that this makes it sufficiently clear that the -nokeycheck option exists.

[toothrot]

/cc @kevinburke