Fix running docs site with docker (#5512)

* Update docs site local build

Clean up makefile

Ignore container-image.sentinel

Fix hugo server errors

Ignore files

Add makefile credit

* Indentation per feedback

* Address PR feedback. Remove sentinel file

* Remove change to .gitignore

site/scripts/hash-files.sh

@@ -0,0 +1,10 @@
+#!/bin/sh
+# this script emits as hash for the files listed in $@
+if command -v shasum >/dev/null 2>&1; then
+  cat "$@" | shasum -a 256 | cut -d' ' -f1
+elif command -v sha256sum >/dev/null 2>&1; then
+  cat "$@" | sha256sum | cut -d' ' -f1
+else
+  echo "missing shasum tool" 1>&2
+  exit 1
+fi