Add a README.

Kick off some basic dev info by documenting the new error handling.

README.md

@@ -0,0 +1,50 @@
+DMDirc
+================================================================================
+
+DMDirc is an IRC client written in Java. It's cross-platform, hugely
+configurable, and is easily extensible with a robust plugins system.
+
+This repository contains the 'core' of the client. If you're interested in
+developing DMDirc or building it from scratch, you'd be much better off
+cloning the [meta](https://github.com/DMDirc/meta) repository, which contains
+the core, plugins, IRC library, etc. Detailed setup instructions are available
+there as well.
+
+Development information
+--------------------------------------------------------------------------------
+
+### Error handling
+
+DMDirc has a user interface for displaying details of errors to users. It also
+supports uploading of errors to the
+[DMDirc sentry instance](https://sentry.dmdirc.com/) if the user allows it (or
+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).
+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),
+and also whether the error is fatal or not.
+
+A typical class that reports errors will look something like the following:
+```java
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import static com.dmdirc.util.LogUtils.APP_ERROR;
+
+public class MyClass {
+
+    private static final Logger LOG = LoggerFactory.getLogger(MyClass.class);
+
+    public void doSomething() {
+        try {
+            // Do something
+        } catch (SomeException ex) {
+            LOG.error(APP_ERROR, "Couldn't do something!", ex);
+        }
+    }
+
+}
+```