[add-cloud,LXD] Interactive mode outputs final text that can be improved

[Peter Matulis]

Invoking `add-cloud` and choosing 'lxd' will lead to this final text being printed:

===
You may need to `juju add-credential lxd-remote' if your cloud needs additional credentials
Then you can bootstrap with 'juju bootstrap lxd-remote'
===

I realize that, barring injecting more intelligence into the software that could lead to customised text, we want a simple template that covers all cases, but the only time new credentials are not needed is for the localhost cloud.

I also question the use of the verb "bootstrap" to guide users. It is technical jargon that should be avoided.

Suggestion:

===
You will need to add credentials for this cloud (`juju add-credential lxd-remote`) before creating a controller (`juju bootstrap lxd-remote`).
===

Corner cases not considered:

1. Adding a new localhost cloud (which the current template probably does not handle well)
2. If possible: Add credentials for cloud X, remove cloud X, add cloud X, and reuse the original credentials (i.e. credentials may not need to be added).

At the very least, please be consistent with the use of backticks (or single quotes) and add full stops to the end of each sentence.

I didn't test this on other clouds but I'm guessing the template is the same.

[Peter Matulis (petermatulis)]

https://github.com/juju/juju/pull/9271