Improve tooltip on DNS name field (and maybe title)

[irl]

#18342 has a discussion on the semantics of the host_name field.

[karsten]

Tweak summary.

[irl]

Moving this into my queue.

[irl]

-    <dt><span class="tip" title="The DNS name for the relay as found by performing a reverse lookup on its first IP address.">DNS Name</span></dt>
+    <dt><span class="tip" title="Host name as found in a reverse DNS lookup of the relay's first IP address. This field is updated at most once in 12 hours, unless the relay IP add
ress changes. Omitted if the relay IP address was not looked up, if no lookup request was successful yet or if no A record was found matching the PTR record.">DNS Name</span></dt>

karsten: Does this look more accurate?

[karsten]

Pretty much. Some trivial comments:

• I'd write "primary IP address" instead of "first IP address" to indicate that it's not just the first that happens to be listed, but the one that the relay uses to register at the directory authorities.
• arma would probably complain to me about not using the Oxford comma.
• You know that last case with A and PTR records far better than I, so I trust you that it's a good addition. I guess we should also extend the ​Onionoo's host_name field specification to cover that case. Does that make sense?

[irl]

I should go and read the code to be sure. This was mostly based on the discussion in #18342.

[irl]

Ok, I read the Java documentation. It didn't help. Then I looked at StackOverflow.

My description is correct.

Fixed in ce07ca3b784f9b76def9387790731268a5ee4750.