Improve readme

README.md

@@ -1,7 +1,9 @@
 Plugin Framework for Java (PF4J)
 =====================
 [![Travis CI Build Status](https://travis-ci.org/decebals/pf4j.png)](https://travis-ci.org/decebals/pf4j)
+<!--
 [![Coverage Status](https://coveralls.io/repos/decebals/pf4j/badge.svg?branch=master&service=github)](https://coveralls.io/github/decebals/pf4j?branch=master)
+-->
 [![Maven Central](http://img.shields.io/maven-central/v/ro.fortsoft.pf4j/pf4j.svg)](http://search.maven.org/#search|ga|1|pf4j)
 
 A plugin is a way for a third party to extend the functionality of an application. A plugin implements extension points
@@ -186,7 +188,7 @@ protected PluginDescriptorFinder createPluginDescriptorFinder() {
 }
 ```
     
-and in plugin respository you must have a plugin.properties file with the below content:
+and in plugin repository you must have a plugin.properties file with the below content:
 
 ```
 plugin.class=ro.fortsoft.pf4j.demo.welcome.WelcomePlugin
@@ -201,6 +203,24 @@ Also, you can control plugin instance creation overriding `createPluginFactory`
 
 For more information please see the demo sources.
 
+** Note** If your application didn't find extensions then make sure that you have a file with name `extensions.idx` 
+generated by PF4J in the plugin jar.
+It's most likely that they are some problems with the annotation processing mechanism from Java.
+O possible solution to resolve your problem is to add a configuration to your maven build.
+The `maven-compiler-plugin` can be configured to do this like so:
+```
+<plugin>
+    <groupId>org.apache.maven.plugins</groupId>
+    <artifactId>maven-compiler-plugin</artifactId>
+    <version>2.5.1</version>
+    <configuration>
+        <annotationProcessors>
+            <annotationProcessor>ro.fortsoft.pf4j.processor.ExtensionAnnotationProcessor</annotationProcessor>
+        </annotationProcessors>
+    </configuration>
+</plugin> 
+```
+
 Plugin assembly
 ------------------------------
 After you developed a plugin the next step is to deploy it in your application. For this task, one option is to create a zip file with a structure described in section [How to use](https://github.com/decebals/pf4j/blob/master/README.md#how-to-use) from the beginning of the document.  
@@ -376,6 +396,14 @@ You can plug your custom `ExtensionStorage` implementation in `ExtensionAnnotati
 For example if I want to use `ServiceProviderExtensionStorage` then the value for the `pf4j.storageClassName` key must be
 `ro.fortsoft.pf4j.processor.ServiceProviderExtensionStorage`
 
+**NOTE:** `ServiceLoaderExtensionFinder`, the class that lookups for extensions stored in `META-INF/services` folder, is
+not added/enabled by default. To do this please override `createExtensionFinder` from `DefaultPluginManager`:
+```java
+protected ExtensionFinder createExtensionFinder() {
+    return ((DefaultExtensionFinder) super.createExtensionFinder()).addServiceProviderExtensionFinder();
+}
+```
+
 Demo
 -------------------
 I have a tiny demo application. The demo application is in demo folder.