install: add nvm, use that to install yarn

install

@@ -119,6 +119,13 @@ if [ ! -d ~/.tmux/plugins/tpm ] ; then
   fi
 fi
 
-# TODO - install node?
+# Install nvm.
+curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.38.0/install.sh | bash
+
+# We can't stop nvm appending to bashrc, but we don't need it - the variables nvm writes to .bashrc are already in
+# ~/.bashrc.d/nvm.bash
+cp bashrc bashrc-bk
+nvm install node && nvm use node && npm i -g yarn
+cp bashrc-bk bashrc
 
 ./install-vim