Suggestion: Equation labels

[TimArborealis]

Add instructions for equation labelling so they can be referenced in the text. Is there anything else that needs to be done in order for cross-references like this to be possible?

See https://www.w3.org/TR/mathml4/#presm_eqno

[josteinaj]

@GauteR: Denne saken var ikke tilordnet noen. Setter den til deg siden du er eier av dette repoet.

(dette er en automatisk melding)

[TimArborealis]

Closing this issue because it is dealt with in #44 (comment)