io/fs: documentation of func Sub

[hweidner]

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

$ go version
go version go1.16 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/harald/.cache/go-build"
GOENV="/home/harald/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/harald/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/harald/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/golang/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/golang/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.16"
GCCGO="/usr/bin/gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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-build2438140086=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Read the documentation of the func Sub in package io/fs.
https://golang.org/pkg/io/fs/#Sub

What did you expect to see?

See below

What did you see instead?

There is a small bug in the description of what func Sub does. In

Otherwise, Sub returns a new FS implementation sub that, in effect, implements sub.Open(dir) as fsys.Open(path.Join(dir, name)).

I think it should read "sub.Open(name)" instead of "sub.Open(dir)".

[toothrot]

/cc @rsc

[gopherbot]

Change https://golang.org/cl/296389 mentions this issue: io/fs: minor corrections to Sub docs