ensure FetchContent-able

[johnmcfarlane]

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What would you like to see in CNL?

Describe the feature you think is missing.

(This doesn't have to be a new definition or API, but anything about CNL which
is missing such as docs or platform support.)

What are you trying to do?

For context it might help to explain what you're trying to achieve.

What environment are you working in?

What compiler, operating system, project version etc.?
This might help provide some context.
It is also helpful information for understanding who CNL's users are.

What, if any, instructions are you following?

Before you thought to ask this question,
what source(s) of information -- if any -- were you following?