Added nix-shell plugin to oh-my-zsh

pkgs/zsh/plugins/nix-shell/scripts/buildShellShim

@@ -0,0 +1,26 @@
+#! /usr/bin/env sh
+
+if [ "$1" = "--rcfile" ]; then
+  # This means the shell should stay open after executing. So we remove the last line which contains 'exit'
+  shift
+  tmp="$(cat $1)"
+  echo ${tmp%exit} > $1
+  cat >> $1 <<EOF
+SHELL=$NIX_EXECUTING_SHELL
+unset NIX_BUILD_SHELL
+FPATH=\$(echo 'echo \$FPATH' | $NIX_EXECUTING_SHELL --stdin)
+for path in \${PATH//:/ }; do
+  if [[ \$path = /nix/store/* ]]; then
+    path=\${path/%bin/share\/zsh\/site-functions}
+    if [ -d "\$path" ]; then
+      FPATH="\$path:\$FPATH"
+    fi
+  fi
+done
+FPATH=\$FPATH $NIX_EXECUTING_SHELL
+EOF
+  /usr/bin/env bash $1
+else
+  /usr/bin/env bash "$@"
+fi
+