add open collective link to nav bar and footer

[M0nica]

add a "Donate" link to the nav bar -- the link should direct visitors to https://opencollective.com/react-ladies

Also want to add open collective icon and link to the footer:

Here are some related places on GitHub for adding OpenCollective icon
FortAwesome/Font-Awesome#14475
opensourcedesign/opensourcedesign.github.io#232

[M0nica]

I've added open collective link to header but it still needs to be added to the footer.

[M0nica]

It has been added to the header so I will close this issue for now.