Update manual releasing instructions

Author: dead-claudia

MANUAL_UPDATING.md

@@ -0,0 +1,19 @@
+# Manual docs updates
+
+Updates to the site are normally built and published automatically, but manual local updates can be done via `scripts/update-docs.js`.
+
+```bash
+# These steps assume that MithrilJS/mithril.js is a git remote named "mithriljs"
+
+# Ensure your next branch is up to date
+$ git checkout next
+$ git pull mithriljs next
+
+# Manually ensure that no new feature docs were added
+
+$ node scripts/update-docs
+```
+
+After the docs build completes, the updated docs should appear on https://mithril.js.org in a few minutes.
+
+**Note:** When updating the stable version with a release candidate out, ***make sure to update the index + navigation to point to the new stable version!!!***