Update sanitization.md

Document customization of sanitation settings; see https://github.com/gollum/gollum/issues/759

docs/sanitization.md

@@ -2,31 +2,32 @@ Sanitization Rules
 ==================
 
 Gollum uses the [Sanitize](http://wonko.com/post/sanitize) gem for HTML
-sanitization.
+sanitization. Below you find the default allowed tags, attributes, and protocols, as well as directions to customize these settings.
 
-See `lib/gollum.rb` for actual settings.
+# Default Settings
 
 ## ALLOWED TAGS
 
-a, abbr, acronym, address, area, b, big, blockquote, br, button, caption,
-center, cite, code, col, colgroup, dd, del, dfn, dir, div, dl, dt, em,
-fieldset, font, form, h1, h2, h3, h4, h5, h6, hr, i, img, input, ins, kbd,
-label, legend, li, map, menu, ol, optgroup, option, p, pre, q, s, samp,
-select, small, span, strike, strong, sub, sup, table, tbody, td, textarea,
-tfoot, th, thead, tr, tt, u, ul, var
+a, abbr, acronym, address, area, b, big, blockquote, br, button, caption, center, cite, code, col, colgroup, dd, del, dfn, dir, div, dl, dt, em, fieldset, font, form, h1, h2, h3, h4, h5, h6, hr, i, img, input, ins, kbd, label, legend, li, map, menu, ol, optgroup, option, p, pre, q, s, samp, select, small, span, strike, strong, sub, sup, table, tbody, td, textarea, tfoot, th, thead, tr, tt, u, ul, var
 
 ## ALLOWED ATTRIBUTES
 
-abbr, accept, accept-charset, accesskey, action, align, alt, axis, border,
-cellpadding, cellspacing, char, charoff, charset, checked, cite, class, clear,
-cols, colspan, color, compact, coords, datetime, dir, disabled, enctype, for,
-frame, headers, height, href, hreflang, hspace, id, ismap, label, lang,
-longdesc, maxlength, media, method, multiple, name, nohref, noshade, nowrap,
-prompt, readonly, rel, rev, rows, rowspan, rules, scope, selected, shape,
-size, span, src, start, summary, tabindex, target, title, type, usemap,
-valign, value, vspace, width
+a href, abbr, accept, accept-charset, accesskey, action, align, alt, axis, border, cellpadding, cellspacing, char, charoff, class, charset, checked, cite, clear, cols, colspan, color, compact, coords, datetime, dir, disabled, enctype, for, frame, headers, height, hreflang, hspace, id, img src, ismap, label, lang, longdesc, maxlength, media, method, multiple, name, nohref, noshade, nowrap, prompt, readonly, rel, rev, rows, rowspan, rules, scope, selected, shape, size, span, start, summary, tabindex, target, title, type, usemap, valign, value, vspace, width
 
 ## ALLOWED PROTOCOLS
 
-a href: http, https, mailto
-img src: http, https
+a href: http, https, mailto, ftp, irc, apt, :relative
+img src: http, https, :relative
+form action: http, https, :relative
+
+# Customizing
+
+To customize these settings, edit your `config.rb` file along the following lines (be sure to run gollum with the `--config` option):
+
+```ruby
+sanitizer = Gollum::Sanitization.new
+sanitizer.protocols['a']['href'].concat ['ssh', 'vnc'] # Protocols
+sanitizer.elements.concat ['customtag1', 'customtag2'] # Tags
+sanitizer.attributes['a'].push 'target' # Attributes
+Precious::App.set(:wiki_options, {:sanitization => sanitizer})
+```