Add executeFunction example to readme
Add executeFunction example to readme

[Finishes #77043436]

gemfire/node-gemfire,gemfire/node-gemfire,mross-pivotal/node-gemfire,mross-pivotal/node-gemfire,gemfire/node-gemfire,gemfire/node-gemfire,mross-pivotal/node-gemfire,mross-pivotal/node-gemfire,mross-pivotal/node-gemfire,mross-pivotal/node-gemfire,gemfire/node-gemfire,gemfire/node-gemfire