"Hair It Is: A List of Hair Words". What are the rules for this header? Why is the noun before it is? Intuitively, I understand the meaning of this header. But please explain it for certainty.
'Hair it is', as well as utilising a pun, is the construction reasonably often encountered in pronouncements such as
Batman it is.
Bognor Regis it is!
The theatre it is [, then].
Beans on toast it is.
This is equivalent to "So what we've decided on / to watch / to do / to have for supper ... is...
It's an idiomatic inversion of 'It is beans on toast' ('What we've decided on is beans on toast', where 'it' is semi-referential.
'Hair it is', punning on 'Here it is', uses 'it' even less referentially. As other answers imply, analysing beyond the echoing of 'here it is' is arguably unnecessary.
'A list of hair words' is just a fragment (here, [traditionally] a noun phrase), licensed after a colon.
The first 'Hair' seems to be a homophonic pun on the word 'here', since the article is presumably about...hair?
In the phrase 'hair it is', 'hair' is a pun (a verbal joke) for 'here', and should be considered to function like 'here', as an adverb.