Add Cache-Control "public,max-age=0,must-revalidate" to index.html in SPA Example (#410)

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

src/docs/markdown/caddyfile/patterns.md

@@ -241,6 +241,15 @@ example.com {
 }
 ```
 
+If your `index.html` is static, you may want to consider adding a `Cache-Control` header to instruct clients to cache it. Since the `try_files` rewrite is used to serve it from other paths, you can wrap the `try_files` with a `route` so that the `header` handler runs after the rewrite (it normally would run before due to the [directive order](/docs/caddyfile/directives#directive-order)):
+
+```caddy-d
+route {
+	try_files {path} /index.html
+	header /index.html Cache-Control "public, max-age=0, must-revalidate"
+}
+```
+
 
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