updates to pointCNN guide - due to new features and workflow changes. (#1061)

* Major updates to pointCNN guide

added tips for new features.
removed obsolete tips.
added 3D DL tools info.
added deprecation info.
polished env. setup steps.
improved coherence about the term 'classification'

* changes suggested by divyansh

* added 'conda update conda' as per recent discussions

Author: vbhv14