Update configuring.asciidoc with per-domain settings

doc/help/configuring.asciidoc

@@ -63,6 +63,10 @@ customizable.
 Using the link:commands.html#set[`:set`] command and command completion, you
 can quickly set settings interactively, for example `:set tabs.position left`.
 
+Some settings are also customizable for a given
+https://developer.chrome.com/apps/match_patterns[URL pattern] by doing e.g.
+`:set --pattern=*://example.com/ content.images false`.
+
 To get more help about a setting, use e.g. `:help tabs.position`.
 
 To bind and unbind keys, you can use the link:commands.html#bind[`:bind`] and
@@ -147,7 +151,6 @@ prefix to preserve backslashes) or a Python regex object:
 If you want to read a setting, you can use the `c` object to do so as well:
 `c.colors.tabs.even.bg = c.colors.tabs.odd.bg`.
 
-
 Using strings for setting names
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -171,6 +174,17 @@ To read a setting, use the `config.get` method:
 color = config.get('colors.completion.fg')
 ----
 
+Per-domain settings
+~~~~~~~~~~~~~~~~~~~
+
+Using `config.set`, some settings are also customizable for a given
+https://developer.chrome.com/apps/match_patterns[URL pattern]:
+
+[source,python]
+----
+config.set('content.images', False, '*://example.com/')
+----
+
 Binding keys
 ~~~~~~~~~~~~