add switch_remote.sh script and update docs accordingly

switch_remote.sh

@@ -0,0 +1,14 @@
+#/usr/bin/env bash
+# a small script for calling nixos-rebuild switch on a remote host but with less repitition
+set -euo pipefail
+
+ACTION=$1
+HOST=$2
+
+exec nixos-rebuild $ACTION \
+  --use-substitutes \
+  --no-build-nix \
+  --use-remote-sudo \
+  --build-host "$HOST" \
+  --target-host "$HOST" \
+  --flake ".#$HOST" \