Add example for Log4j ECS Layout (#95)

Author: Victor Laborie

log4j-ecs-layout/README.md

@@ -16,3 +16,33 @@ Add a dependency to your application
 If you are not using a dependency management tool, like maven, you have to add both,
 `log4j-ecs-layout` and `ecs-logging-core` jars manually to the classpath.
 For example to the `$CATALINA_HOME/lib` directory.
+
+## Step 2: use the `EcsLayout`
+
+Instead of the usual layout class `"org.apache.log4j.PatternLayout"`, use `"co.elastic.logging.log4j.EcsLayout"`.
+
+## Example
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE log4j:configuration SYSTEM "log4j.dtd">
+<log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
+    <appender name="LogToConsole" class="org.apache.log4j.ConsoleAppender">
+        <param name="Target" value="System.out"/>
+            <layout class="co.elastic.logging.log4j.EcsLayout">
+                <param name="serviceName" value="my-app"/>
+            </layout>
+    </appender>
+    <appender name="LogToFile" class="org.apache.log4j.RollingFileAppender">
+        <param name="File" value="logs/app.log"/>
+            <layout class="co.elastic.logging.log4j.EcsLayout">
+                <param name="serviceName" value="my-app"/>
+            </layout>
+    </appender>
+    <root>
+        <priority value="INFO"/>
+        <appender-ref ref="LogToFile"/>
+        <appender-ref ref="LogToConsole"/>
+    </root>
+</log4j:configuration>
+```