Update example README.md

examples/README.md

 # Official DGL Examples and Modules
 
+The folder contains example implementations of selected research papers related to Graph Neural Networks. Note that the examples may not work with incompatible DGL versions.
+* For examples working with the latest master (or the latest [nightly build](https://www.dgl.ai/pages/start.html)), check out https://github.com/dmlc/dgl/tree/master/examples.
+* For examples working with a certain release, check out `https://github.com/dmlc/dgl/tree/<release_version>/examples` (E.g., https://github.com/dmlc/dgl/tree/0.5.x/examples)
+
 ## Overview
 
 | Paper                                                        | node classification | link prediction / classification | graph property prediction | sampling           | OGB                |