avformat/dashenc: Add documentation for http method option

doc/muxers.texi

@@ -252,6 +252,8 @@ DASH-templated name to used for the initialization segment. Default is "init-str
 DASH-templated name to used for the media segments. Default is "chunk-stream$RepresentationID$-$Number%05d$.m4s"
 @item -utc_timing_url @var{utc_url}
 URL of the page that will return the UTC timestamp in ISO format. Example: "https://time.akamai.com/?iso"
+@item method @var{method}
+Use the given HTTP method to create output files. Generally set to PUT or POST.
 @item -http_user_agent @var{user_agent}
 Override User-Agent field in HTTP header. Applicable only for HTTP output.
 @item -http_persistent @var{http_persistent}