Issue #6330 - Improve javadoc for CustomRequestLog %H

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>

jetty-server/src/main/java/org/eclipse/jetty/server/CustomRequestLog.java

@@ -152,7 +152,9 @@ import static java.lang.invoke.MethodType.methodType;
  *
  * <tr>
  * <td valign="top">%H</td>
- * <td>The request protocol.</td>
+ * <td>Returns the name and version of the protocol the request uses in the form
+ * protocol/majorVersion.minorVersion, for example, HTTP/1.1. For HTTP servlets,
+ * the value returned is the same as the value of the CGI variable SERVER_PROTOCOL.</td>
  * </tr>
  *
  * <tr>