Guide need to be added for `How to use OnShape Java Client`

[sunilgulabani]

Onshape online community is not that matured that we get help from there so guide need to be added for How to use OnShape Java Client. As developer can't dig into library code to find which classes are used for which purpose. There should be short example saying - For Authentication we need to use particular class, to upload file we need to use particular code snippet and like wise.