Update R template - Migrated to a self hosted repo by the community author

.github/workflows/test-pr.yaml

@@ -46,7 +46,6 @@ jobs:
             perl: ./**/perl/**
             puppet: ./**/puppet/**
             python-3-pypy: ./**/python-3-pypy/**
-            r: ./**/r/**
             reasonml: ./**/reasonml/**
             ruby-rails: ./**/ruby-rails/**
             ruby-sinatra: ./**/ruby-sinatra/**

containers/r/README.md

@@ -1,3 +1,5 @@
+**IMPORTANT NOTE: The `R` template is now hosted by the community author in the repo [rocker-org/devcontainer-templates](https://github.com/rocker-org/devcontainer-templates/tree/main/src/r-ver).**
+
 # R (Community)
 
 ## Summary