docs: Expand install into multiple pages; add example to header docs

src/docs/markdown/caddyfile/directives/header.md

@@ -65,4 +65,13 @@ header {
 	# keep referrer data off of HTTP connections
 	Referrer-Policy no-referrer-when-downgrade
 }
-```
+```
+
+Multiple header directives that are intended to be mutually-exclusive:
+
+```
+route {
+	header           Cache-Control max=age=3600
+	header /static/* Cache-Control max=age=31536000
+}
+```