error docs.

docs/Error/ErrorHandler.md

@@ -0,0 +1,46 @@
+# Improved version of ErrorHandler
+
+The main goal of the error.log is to notify about internal errors of the system.
+By default there would also be a lot of noise in there.
+
+Most 404 logs should not be part of your error log, for example. 
+You can either completely ignore them, or better yet put them into their own space:
+```php
+Log::config('404', [
+	'className' => 'DatabaseLog.Database',
+	'type' => '404',
+	'levels' => ['error'],
+	'scopes' => ['404'],
+]);
+```
+
+Make sure your other log configs are scope-deactivated then to prevent them being logged twice:
+```php
+	'Log' => [
+		'debug' => [
+			'scopes' => false,
+			...
+		],
+		'error' => [
+			'scopes' => false,
+			...
+		],
+	],
+```
+
+In your bootstrap, the following snippet just needs to include the ErrorHandler of this plugin:
+````php
+// Switch Cake\Error\ErrorHandler to
+use Tools\Error\ErrorHandler;
+
+if ($isCli) {
+	(new ConsoleErrorHandler(Configure::read('Error')))->register();
+} else {
+	(new ErrorHandler(Configure::read('Error')))->register();
+}
+```
+
+### Tips
+You should also set up a monitor to check for internally caused 404s (referrer is a page on the own site) and alert (via email or alike).
+In that case you are having invalid links in your pages somewhere, which should be fixed.
+All other 404s are caused from the outside (often times crawlers and bots) and are usually not too relevant.

docs/README.md

@@ -12,6 +12,7 @@ This cake3 branch only works for **CakePHP3.x** - please use the master branch f
 * [Upgrade guide from 2.x to 3.x](Upgrade.md)
 
 ## Detailed Documentation - Quicklinks
+* [ErrorHandler](Error/ErrorHandler.md)
 * [Behavior/Jsonable](Behavior/Jsonable.md)
 * [Behavior/Passwordable](Behavior/Passwordable.md)
 * [Behavior/Slugged](Behavior/Slugged.md)