docs: Update for v2.2

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

@@ -0,0 +1,66 @@
+---
+title: push (Caddyfile directive)
+---
+
+# push
+
+Configures the server to pre-emptively send resources to the client using HTTP/2 server push.
+
+Resources can be linked for server push by specifying the Link header(s) of the response. This directive will automatically push resources described by upstream Link headers in these formats:
+
+- `<resource>; as=script`
+- `<resource>; as=script,<resource>; as=style`
+- `<resource>; nopush`
+- `<resource>;<resource2>;...`
+
+where `<resource>` begins with a forward slash `/` (i.e. is a URI path with the same host). Only same-host resources can be pushed. If a linked resource is external or if it has the `nopush` attribute, it will not be pushed.
+
+By default, push requests will include some headers deemed safe to copy from the original request:
+
+- Accept-Encoding
+- Accept-Language
+- Accept
+- Cache-Control
+- User-Agent
+
+as it is assumed many requests would fail without these headers; these do not need to be configured manually.
+
+Push requests are virtualized internally, so they are very lightweight.
+
+
+## Syntax
+
+```caddy-d
+push [<matcher>] [<resource>] {
+	[GET|HEAD] <resource>
+	headers {
+		[+]<field> [<value|regexp> [<replacement>]]
+		-<field>
+	}
+}
+```
+
+- **&lt;resource&gt;** is the target URI path to push. If used within the block, may optionally be preceeded by the method (GET or POST; GET is default).
+- **&lt;headers&gt;** manipulates the headers of the push request using the same syntax as the [`header` directive](/docs/caddyfile/directives/header). Some headers are carried over by default and do not need to be explicitly configured (see above).
+
+
+
+## Examples
+
+Push any resources described by `Link` headers in the response:
+
+```caddy-d
+push
+```
+
+Same, but also push `/resources/style.css` for all requests:
+
+```caddy-d
+push * /resources/style.css
+```
+
+Push `/foo.jpg` only when `/foo.html` is requested by the client:
+
+```caddy-d
+push /foo.html /foo.jpg
+```