There are some examples on issue #850 of using this feature, but they
are not easily found from the documentation. Adding them here as an
example makes them more findable and ensures they keep working if the
API changes.

This took me some time to figure out so document for others.

Some notes on the configuration options chosen:

* We want `AllowShortEnumsOnASingleLine` set to `false`, but that
option is clang-format-11 and up, which is not out yet.
* `IndentPPDirectives` is currently inconsistent, but `AfterHash`
is the preferred style in new code.
* `NamespaceIndentation` is a mess, but `All` is closer to the effect
we want than `Inner`.
* `SpacesInParentheses` set to `true` is not ideal due to it also
introducing extra spaces in preprocessor expressions, but using it
is much closer to the current style than not.

All in all, using this setting globally would reformat pretty much
every line of code in the codebase, but it is as close as possible
to the bespoke style currently used. Still, it should only be used
on the diffs.

Closes #1182

On systems where the file system has excute permissions, this script was
not marked as executable in a clean git checkout and so could be run
without first changing the permissions. Fixed by setting the relevant
git flag.