note source of project list

howto/puppet.md

@@ -1049,6 +1049,9 @@ be validated but could address that issue:
  * [lp2r10k](https://github.com/dharmabruce/lp2r10k/): convert "librarian" `Puppetfile` (missing
    dependencies) into a "r10k" `Puppetfile` (with dependencies)
 
+Note that this list comes from the [updating your Puppetfile](https://github.com/puppetlabs/r10k/blob/master/doc/updating-your-puppetfile.mkd#automatic-updates)
+documentation in the r10k project, which is also relevant here.
+
 ### Authenticate code with checksums
 
 This part is the main problem with moving away from a monorepo. By