hgrc.5: explain order of mail.charsets
TODO: add mail.charsets section to hgrc.5.ja.txt
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<link rel="icon" href="#staticurl#hgicon.png" type="image/png">
<meta name="robots" content="index, nofollow" />
<link rel="stylesheet" href="#staticurl#style.css" type="text/css" />