Updating PoshC2

It is not recommended to update PoshC2 during an engagement. Incoming changes may be incompatible with an existing project and can result in erratic behaviour.

When using a git cloned version of PoshC2 you can update your PoshC2 installation using the following command:

*** PoshC2 Update Script ***
Usage:
posh-update -b <git branch>

Default is the master branch

Any existing changes are `git stash`ed before updating.