added btn for back-to-top feature
added btn for back-to-top feature

NashvilleWomenProgrammers/nashvillewomenprogrammers.github.io,NashvilleWomenProgrammers/nwp-site-v2,NashvilleWomenProgrammers/nashvillewomenprogrammers.github.io,NashvilleWomenProgrammers/nwp-site-v2