ssh-agent on Windows Subsystem for Linux

It took a lot of googling to finally find a solution for setting up ssh-agent properly on WSL, so I'm not entering my ssh passphrase every time I do anything requiring it. Add this to your profile (.bashrc or .zshrc):

eval $(ssh-agent -s)
ssh-add ~/.ssh/id_rsa

Now, when you start a new terminal you'll be asked for your passphrase, and it'll get used automatically in that session!