Add deploy note

docs/how-to-deploy.md

@@ -0,0 +1,8 @@
+1. `cd docs` from repo root
+1. Install the vercel cli if you haven't already
+    - `pnpm i -g vercel`
+1. `vercel` to deploy if you already have the project linked
+1. Otherwise, `vercel login` and `vercel` to link
+    - Choose Zed Industries as the team, then `zed-app-docs` as the project
+
+Someone can write a script for this when they have time.