README: add pkg.go.dev docs link

As generated by https://pkg.go.dev/badge/

While at it, update the old doc URL in the text
(currently, godoc.org redirects to pkg.go.dev).

Signed-off-by: Kir Kolyshkin <[email protected]>
Acked-by: Tom Hromatka <[email protected]>
[PM: break up the long lines]
Signed-off-by: Paul Moore <[email protected]>

Author: kolyshkin

README.md

@@ -2,6 +2,7 @@
 ===============================================================================
 https://github.com/seccomp/libseccomp-golang
 
+[![Go Reference](https://pkg.go.dev/badge/github.com/seccomp/libseccomp-golang.svg)](https://pkg.go.dev/github.com/seccomp/libseccomp-golang)
 [![validate](https://github.com/seccomp/libseccomp-golang/actions/workflows/validate.yml/badge.svg)](https://github.com/seccomp/libseccomp-golang/actions/workflows/validate.yml)
 [![test](https://github.com/seccomp/libseccomp-golang/actions/workflows/test.yml/badge.svg)](https://github.com/seccomp/libseccomp-golang/actions/workflows/test.yml)
 
@@ -27,9 +28,9 @@ list.
 
 * https://groups.google.com/d/forum/libseccomp
 
-Documentation is also available at:
+Documentation for this package is also available at:
 
-* https://godoc.org/github.com/seccomp/libseccomp-golang
+* https://pkg.go.dev/github.com/seccomp/libseccomp-golang
 
 ## Installing the package