Include --post302 in create go-link with curl example

The example uses `(http://)go` rather than `https://go.[tailnet]` (hence using `-L`), however by default `curl` swaps from `POST` to `GET` on a 302 unless [`--post302`](https://manpages.debian.org/curl#post302) is passed, causing the example command to fail to create a new link.

Signed-off-by: Michael Diamond <[email protected]>

Author: dimo414

tmpl/help.html

@@ -137,7 +137,7 @@ <h2 id="api">Application Programming Interface (API)</h2>
 <p>
 Create a new link by sending a POST request with a <code>short</code> and <code>long</code> value:
 
-<pre>$ curl -L -H Sec-Golink:1 -d short=cs -d long=https://cs.github.com/ {{go}}
+<pre>$ curl -L --post302 -H Sec-Golink:1 -d short=cs -d long=https://cs.github.com/ {{go}}
 {{`{"Short":"cs","Long":"https://cs.github.com/","Created":"2022-06-03T22:15:29.993978392Z","LastEdit":"2022-06-03T22:15:29.993978392Z","Owner":"[email protected]"}`}}
 </pre>