maps: add examples for All, Keys, Values, Insert, and Collect functions
Change-Id: I4ee61bea9997b822aa1ec2cc3d01b4db5f101e4c
GitHub-Last-Rev:
d88282a92ec86721356696108898e06924ec89c9
GitHub-Pull-Request: golang/go#68696
Reviewed-on: https://go-review.googlesource.com/c/go/+/602315
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>