Merge pull request #1641 from eclipse/DOC-375

Add readme to plugins

plugins/README.md

@@ -0,0 +1,15 @@
+## How to Build Plugins?
+
+In plugin root directory, run:
+
+`mvn clean install`
+
+## How to Add Custom Plugin to Modules Build Cycle?
+
+Add a module to plugins parent pom.xml:
+
+`<module>your-plugin-name</module>`
+
+## How to Add a Custom Plugin to Che Assembly?
+
+See: [Building Custom Assemblies] (https://eclipse-che.readme.io/docs/plug-ins#add-plug-in-by-referencing-from-che)