add invidious companion temporary doc (#620)

docs/companion-caddy.md

@@ -0,0 +1,22 @@
+# Caddy reverse proxy setup with Invidious companion
+
+This is a very basic config, assuming that you're using Caddy to manage SSL certificates for you.
+Any log is disabled by default. Do not forget to replace `server_name` with your domain.
+
+```
+https://<server_name> {
+
+  @companion {
+		path /latest_version
+		path /api/manifest/dash/id/*
+		path /videoplayback*
+	}
+
+  reverse_proxy @companion localhost:8282
+  reverse_proxy localhost:3000
+
+  log {
+      output discard
+  }
+}
+```