cmd/releaseschedule: basic doc and README.md

"cmd/releaseschedule" had no docs and no direction on what to do with
the output. Would be better to have links to the wiki page and basic
information on what to do with the output. Helps with discoverability as
well if someone searches for information that SVG.

Add package doc with request to update wiki & links to wiki. Generate
README.md with update-readmes.go.

Fixes golang/go#59314

cmd/releaseschedule/README.md

@@ -0,0 +1,7 @@
+<!-- Auto-generated by x/build/update-readmes.go -->
+
+[![Go Reference](https://pkg.go.dev/badge/golang.org/x/build/cmd/releaseschedule.svg)](https://pkg.go.dev/golang.org/x/build/cmd/releaseschedule)
+
+# golang.org/x/build/cmd/releaseschedule
+
+Releaseschedule generates the release schedule diagram used on the release schedule wiki.

cmd/releaseschedule/main.go

@@ -1,3 +1,11 @@
+// Releaseschedule generates the release schedule diagram used
+// on the release schedule wiki.
+//
+// When this program is updated, regenerate the SVG and replace the old version
+// on the Go Release Cycle wiki page
+//
+// https://go.dev/s/release
+// https://golang.org/wiki/Go-Release-Cycle
 package main
 
 import (