PuppetManifest: Add documentation on how to verify puppet files.

Ideally the `make check` should execute this.
Until then let's document the steps to manually verify the input files.

Units/parser-puppetManifest.r/README

@@ -3,3 +3,28 @@ the quality and usefulness mtable regex metaparser.
 
 Input for test cases started from puppet- under this directory are
 taken from puppet-3.8.7/spec/fixtures/unit/parser/lexer/*.pp.
+
+## Test Input Verification
+
+### Requirements
+
+Install puppet-agent to your platform:
+[Linux](https://puppet.com/docs/puppet/5.3/install_linux.html),
+[Windows](https://puppet.com/docs/puppet/5.3/install_windows.html) or
+[macOS](https://puppet.com/docs/puppet/5.3/install_osx.html)
+
+### Execute Verification
+
+From the `<repo_root>/Units/parser-puppetManifest.r` directory execute the
+following:
+
+```
+find . -name "*.pp" | xargs -n 1 -I@ bash -c " echo @ &&  /opt/puppetlabs/bin/puppet apply --noop @"
+```
+
+In that command we find all puppet files in the unit test directory. Then we
+run `puppet apply --noop` on each of them, essentially checking the input
+file.  The return value of the above command will be non-zero if any puppet
+run fails.
+
+