Add crud example file

[olich97]

Overview

A new file in /example folder.
The file contains a little demonstration on how the document api could be used in CRUD operations context.

Testing recommendations

1. Configure your CouchDB server
2. Configure your settings (url & database name) in createDatabaseConnection function
3. Run:

node crud_operations.js

Checklist

• Code is written and works correctly;
• (N/A) Changes are covered by tests;
• (N/A) Documentation reflects the changes;

[YakovL]

Hey @olich97 , could please you update your example by using .auth instead of feeding creds inside url? (please see #321 – or #174 directly)