Add: Example of how to use metatags

Thanks @tzz
Fix document tags

Remove left-over stuff from copying a different files header.
Fix document ordering

Fix document ordering so that it does not duplicate another position and
so that it comes before custom inventory.
Fix: Rename with proper extension
Add cf3 syntax highlighting

It makes it easier to read.
Merge pull request #904 from nickanderson/3.6-tags

Backport tags tutorial