tooling/ide: added a top-level README.txt

git-svn-id: https://svn.apache.org/repos/asf/sling/branches/tooling-ide-vlt@1525578 13f79535-47bb-0310-9956-ffa450edef68
org.apache.sling.ide.api should not require org.eclipse bundles.

git-svn-id: https://svn.apache.org/repos/asf/sling/branches/tooling-ide-vlt@1525580 13f79535-47bb-0310-9956-ffa450edef68