Adding link to optionvalue.io

[calcsam]

Add OptionValue resource

[jlevy]

Thanks for the addition. Two notes on this:

(1) This is basically a landing page for the product, so I don't think it merits a link for being informative on its own

(2) That said, there's nothing against having a good overview of tools a companies might use, if we have a balanced overview of tools as one bullet point. But there are also others, like captable.io etc. We should assemble them at once.

Do you have familiarity with the landscape of tools and what others should be mentioned?

[jlevy]

Closing in favor of addressing in #69.