Missing descriptions of three vote types listed in index.md

index.md lists eight voting types, with links to explanations on vote_types.html

vote_types.md only has five explanations, lacking explanations for

If these voting types are supported, they should be described.

Added three description areas on vote_types.html, but only found information that I could use to populate one of them.

The website has been reworked in #110. Now we talk about the two supported types (YNA/STV).

If you find we may still describe other vote types, feel free to add some information pages.

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