Hugo has been making this warning for a while
WARN found no layout file for "html" for kind "term": You should
create a template file which matches Hugo Layouts Lookup Rules for
this combination.
This turned out to be the addition of the `groups:` keyword to the
command frontmatter. Hugo is doing something with this keyword though
this isn't documented in the frontmatter documentation.
The fix was removing the `groups:` keyword from the frontmatter since
it was never used by hugo.
In f544234 we removed the global flags from each command as it was
making each page very big and causing 1000s of lines of duplication in
the man page.
This change adds a new flags page with all the global flags on and
links each command page to it.
Fixes#3273
