docs: publish docs during releases (#2890)

Improvements very welcome for this process. Not sure of a better way to make
sure the right docs get published.

RELEASING.md

@@ -85,8 +85,15 @@ the failures have been resolved.
    c. Tag the repo with the next version: `git tag $NV`.
    d. Push the tag to origin:
       `git push origin $NV`
-2. Update [the releases page](https://github.com/googleapis/google-cloud-go/releases)
+1. Update [the releases page](https://github.com/googleapis/google-cloud-go/releases)
    with the new release, copying the contents of `CHANGES.md`.
+1. Run `go get cloud.google.com/go@vX.Y.Z` then wait for the release
+   to show up on http://pkg.go.dev/cloud.google.com/go (a few minutes).
+1. Go to the [doc publishing job](http://go/google-cloud-go-publish-docs) and
+   trigger the job with the following environment variables:
+   `MODULE=cloud.google.com,VERSION=vX.Y.Z`.
+   Replace the version with the value for the module you're
+   releasing. See [`publish_docs.sh`](/internal/kokoro/publish_docs.sh).
 
 # How to release a submodule
 
@@ -122,6 +129,14 @@ To release a submodule:
       `git push origin $NV`
 1. Update [the releases page](https://github.com/googleapis/google-cloud-go/releases)
    with the new release, copying the contents of `datastore/CHANGES.md`.
+1. Run `go get cloud.google.com/go/datastore@vX.Y.Z` then wait for the release
+   to show up on http://pkg.go.dev/cloud.google.com/go/datastore (a few
+   minutes).
+1. Go to the [doc publishing job](http://go/google-cloud-go-publish-docs) and
+   trigger the job with the following environment variables:
+   `MODULE=cloud.google.com/datastore,VERSION=vX.Y.Z`.
+   Replace the module path and version with the values for the module you're
+   releasing. See [`publish_docs.sh`](/internal/kokoro/publish_docs.sh).
 
 # Appendix