fix for mailto in docs

[endymion1818]

I hope I'm not making a newbie mistake here but the docs refer to the prop mailto on an <a> tag, but my React for Chrome Devtools says this property is invalid ... so I've changed it to a href with mailto: at the start of the link string.

Really hope this is ok...!

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[KyleAMathews]

Ohh! Nope this is correct, thanks!

[jlengstorf]

Hiya @endymion1818! 👋

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