update: Add cloud-boothook tip for user data

[ramimac]

Throwing this up, but let me know if I'm missing something - we're outside my wheelhouse :).

My understanding is #cloud-boothook is a straightforwardly better approach than the current documented cloud-config, and also is what dagrz uses in the linked source

[Frichetten]

What about #cloud-boothook makes it a better approach? :o Here, we set the parameter to always so it runs each time the instance is restarted. I think that's the same as #cloud-boothook?

I'm not opposed to the addition, just want to make sure I understand.

[ramimac]

I left the current details because I think it's useful to present both. Functionally, they're similar (as far as I know). I find it much easier to mentally model, remember, and use the one-line prefix ("Add #cloud-boothook, then your commands, at the top of user data") than the current guidance.

Maybe just a matter of preference? Either way I think including #cloud-boothook somehow will be useful, no strong feelings on how/where!

[Frichetten]

Gotcha, no worries, that sounds reasonable to me! I'll merge this PR and add an item to include an example for #cloud-boothook. Thank you for contributing!