nlist.3: Move deprecation notice to its section

[ziaee]

Summary

Its more clear and good practice for the first sentence of a description
to describe what something is, because there are a lot of different use
cases for documentation.

Fixes: 94b7a335683abcbcd76e8b67d37e21271d81590c

[emaste]

It's not really a deprecation notice though, and we will presumably never remove this function. If you'd rather have it at the end of the description that's fine with me.

[ziaee]

Thanks @emaste! What about this?