curl.1: extend the -X, --request description

docs/curl.1

@@ -1631,6 +1631,14 @@ details and explanations. Common additional HTTP requests include PUT and
 DELETE, but related technologies like WebDAV offers PROPFIND, COPY, MOVE and
 more.
 
+Normally you don't need this option. All sorts of GET, HEAD, POST and PUT
+requests are rather invoked by using dedicated command line options.
+
+This option only changes the actual word used in the HTTP request, it does not
+alter the way curl behaves. So for example if you want to make a proper HEAD
+request, using -X HEAD will not suffice. You need to use the \fI-I, --head\fP
+option.
+
 (FTP)
 Specifies a custom FTP command to use instead of LIST when doing file lists
 with FTP.