Update ContributorTasks.md

[nwanduka]

Added the subsections:

1. how to clone a repository
2. installing docker
3. running camicroscope in docker

Summary

The Introductory tasks in this file involve cloning the camicrosope repositories, installing docker desktop, and running camicroscope in docker but there is no clear guide on how to do these.

Motivation

1. caMicroscope has non-technical and first-time contributors who may not be familiar with Github and its terminologies.
2. While these contributors can, on their own, browse how these actions can be done, it would greatly improve their experience with the project to have all the information they need in one place without having to switch between tabs.

PS: There is no open issue associated with this PR.