Update go.mod and readme

Author: ancientlore

README.md

@@ -1,5 +1,7 @@
 # cachefs
 
+[![Go Reference](https://pkg.go.dev/badge/github.com/ancientlore/cachefs.svg)](https://pkg.go.dev/github.com/ancientlore/cachefs)
+
 Package `cachefs` implements a read-only cache around a `fs.FS`, using `groupcache`.
 
 Using `cachefs` is straightforward:

go.mod

@@ -1,6 +1,6 @@
 module github.com/ancientlore/cachefs
 
-go 1.17
+go 1.19
 
 require (
 	github.com/golang/groupcache v0.0.0-20210331224755-41bb18bfe9da