Add info about how to display text...

README.md

 Development information
 --------------------------------------------------------------------------------
 
+### Displaying text
+
+Text shown in windows (channels, servers, etc) is generated automatically from
+certain types of events passed on the DMDirc event bus. Any event that subclasses
+`DisplayableEvent` can potentially be formatted.
+
+DisplayableEvents are listened for by each window's [`BackBuffer`](https://github.com/DMDirc/DMDirc/blob/master/src/com/dmdirc/ui/messages/BackBuffer.java)
+instance. A format is then applied to the event to transform it into one or more strings. Formats
+are specified in [a YAML file included in the DMDirc jar](https://github.com/DMDirc/DMDirc/blob/master/res/com/dmdirc/ui/messages/format.yml),
+and can be overridden by the user by putting a `format.yml` file in their DMDirc config directory.
+
+A couple of typical formatting entries looks like this:
+
+```yaml
+ChannelMessageEvent:
+  format: "<{{client.modePrefixedNickname}}> {{message}}"
+ChannelModeNoticeEvent:
+  format: "-{{client.modePrefixedNickname}}:{{prefix}}{{channel.name}}- {{message}}"
+  colour: 5
+```
+
+The `{{..}}` templates retrieve properties from the event itself. `{{client.modePrefixedNickname}}`
+is the equivalent of calling `getClient().getModePrefixedNickname().toString()` on the event object.
+
 ### Error handling
 
 DMDirc has a user interface for displaying details of errors to users. It also
 manually clicks on send).
 
 Errors should be logged using a [Slf4j](http://www.slf4j.org/) logger, and
-marked with one markers defined in [LogUtils](https://github.com/DMDirc/DMDirc/blob/master/src/com/dmdirc/util/LogUtils.java).
+marked with one markers defined in [`LogUtils`](https://github.com/DMDirc/DMDirc/blob/master/src/com/dmdirc/util/LogUtils.java).
 These markers allow developers to specify whether an error is an "Application"
 error (which will get reported and should ultimately be fixed), or a "User"
 error (which is due to a problem with the user's config, environment, etc),