Updating the readme

Giving some initial context to these plugins.  Trying help untangle when to use certain gradle plugins and for what reason.

Author: ctoestreich

grails-gsp/README.md

@@ -1,2 +1,18 @@
-## grails-gsp
+## Grails GSP Gradle Plugin 
 
+This gradle plugin is required for all grails 3 applications and plugins that require GSP processing.  If your project includes GSPs you should add the following to your `build.gradle`.
+
+``` gradle
+apply plugin: "org.grails.grails-gsp"
+```
+
+It is typical of standard grails 3 application to use this in conjunction with `grails-web` as in the following example: 
+
+``` gradle
+apply plugin: "org.grails.grails-web"
+apply plugin: "org.grails.grails-gsp"
+```
+
+Dependencies
+-----
+To see what additional plugins will be included with this plugin you can view this project's [build.gradle](https://github.com/grails/grails-core/blob/master/grails-gsp/build.gradle)