os: add examples for Mkdir and MkdirAll
Provides example using value for the perm argument that matches the value set by the mkdir command on MacOS and Linux.
Change-Id: I98d9ac9668de4dc0efde2484f5b00d005628ac9e
GitHub-Last-Rev:
44e617912f3604f4cc05a946d76cd3020acfd722
GitHub-Pull-Request: golang/go#50641
Reviewed-on: https://go-review.googlesource.com/c/go/+/378874
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Trust: Cherry Mui <cherryyz@google.com>