tBTC website about page mentions price peg instead of volume peg

[Naxsun]

I also made a PR for this but I'm not 100% sure I did that correctly so made this issue for it.

In the 'about' page on the tBTC page it states that tBTC is price pegged to BTC.

Was: tBTC is a fully Bitcoin-backed ERC-20 token pegged to the price of Bitcoin.

Proposed: tBTC is a fully Bitcoin-backed ERC-20 token with a volume peg to BTC, meaning 1 TBTC will always equal 1 BTC.