add info about enable/disable plugins

README.md

@@ -150,6 +150,39 @@ and in plugin respository you must have a plugin.properties file with the below
 
 For more information please see the demo sources.
 
+Enable/Disable plugins
+-------------------
+In theory, it's a relation 1:N between an extension point and the extensions for this extension point.
+This works well, except for when you develop multiple plugins for this extension point as different options for your clients to decide on which one to use.
+In this situation you wish a possibility to disable all but one extension.
+For example I have an extension point for sending mail (EmailSender interface) with two extensions: one based on Sendgrid and another
+based on Amazon Simple Email Service. The first extension is located in Plugin1 and the second extension is located in Plugin2.
+I want to go only with one extension (1:1 relation between extension point and extensions) and to achieve this I have two options:
+1) uninstall Plugin1 or Plugin2 (remove from plugins folder pluginX.zip and pluginX folder)
+2) disable Plugin1 or Plugin2
+
+For option two you must create a simple file enabled.txt or disabled.txt in your plugins folder.
+The content for enabled.txt is similar with:
+
+    ########################################
+    # - load only these plugins
+    # - add one plugin id on each line
+    # - put this file in plugins folder
+    ########################################
+    welcome-plugin
+
+The content for disabled.txt is similar with:
+
+    ########################################
+    # - load all plugins except these
+    # - add one plugin id on each line
+    # - put this file in plugins folder
+    ########################################
+    welcome-plugin
+
+All comment lines (line that start with # character) are ignored.
+If a file with enabled.txt exists than disabled.txt is ignored.
+
 Demo
 -------------------
 I have a tiny demo application. The demo application is in demo folder.