update prerequisites page

[joshdentremont]

Purpose / why

When I first started with Islandora I was new to most of the different pieces of software involved. I found it hard to differentiate between Islandora and the other components, but the more I learned about Docker the more I realized that there is nothing special happening for Islandora, it's all a fairly standard Docker / Docker Compose setup for a Drupal site.

This is meant for people who are new to Docker, Composer, Drush, etc. to learn a little bit about what each tool is for and how it is used in the context of Islandora. Ideally they will find resources to help them learn more about each part, but most of that is outside the scope of Islandora / Isle. The goal here is to just give people a nudge in the right direction, and point to some helpful resources like the Islandora YouTube channel and the Drupal Docs.

What changes were made?

Added a list of software involved in the ISLE setup process and what its purpose is.

Verification

There shouldn't be much that needs verification, but if there's anything I'm missing please let me know and I am happy to expand this.

Interested Parties

• @Islandora/documentation
• @Islandora/committers

Checklist

Pull-request Reviewer

Pull-request reviewer should ensure the following:

• Does this PR link to related issues?
• Does the proposed documentation align with the Islandora Documentation Style Guide?
• Are the changes accurate, useful, free of typos, etc?

Person Merging

The person merging should ensure the following:

• Does mkdocs still build successfully? (This is indicated by TravisCI passing. To test locally, and see warnings, see How To Build Documentation.)
• If pages are renamed or removed, have all internal links to those pages been fixed?
• If pages are added, have they been linked to or placed in the menu?
• Did the PR receive at least one approval from a committer, and all issues raised have been addressed?