UPDATED: Add items and commentary to the Resources sections

[chalmerlowe]

Add appropriate links.
Provide summary statements for any links without such statements.

Each of the resources sections should have good resources and each resource should have a link and a brief summary of what students should expect to find when they click on the link.

Several examples:
in the git_config.md file there are two incomplete resources:

• Cheatsheet for Windows command-line commands:
• Cheatsheet for Mac command-line commands:

NOTE: there are two links to cmd/terminal commands included in
prereq_student.md

Ensure that we point students to the right direction and either duplicate the links here OR find some way to deconflict.

in the [git_overview.md] (https://github.com/chalmerlowe/intro_to_sprinting/blob/master/class_materials/git_overview.md) file there appear to be links that do not have a description.

There are assuredly more examples of incomplete resources.