add an update script

[Bhupesh-V]

Is your feature request related to a problem? Please describe.
It would be nice to have an update.sh script in dotman tooling,

• Users should be able to run, dotman update & the latest changes (any new releases) from the repo should be pulled
• To be creative, we can create an auto-updater which looks for updates automatically with a certain frequency of days/weeks and prompts user to install the new update.