Updating information on local testing in the README

[jherrman]

What changes are you introducing?

Expanding and updating the local building information in the README for better usability and easier accessibility by new contributors.

Why are you introducing these changes? (Explanation, links to references, issues, etc.)

The current wording is not very beginner-friendly, and does not mention that you need to have certain packages installed to use the makefile, otherwise it fails (which yields an error that is difficult to interpret, on top of it).

Anything else to add? (Considerations, potential downsides, alternative solutions you have explored, etc.)

It would be ideal to rewrite the information as a procedure with numbered steps, but I don't yet have enough experience with the tooling to do that, so this PR is more of a band-aid (but still, I think, an improvement).

Checklists

• [x] I am okay with my commits getting squashed when you merge this PR.
• [x] I am familiar with the contributing guidelines.

Please cherry-pick my commits into:

• [x] Foreman 3.14/Katello 4.16
• [x] Foreman 3.13/Katello 4.15 (EL9 only)
• [x] Foreman 3.12/Katello 4.14 (Satellite 6.16)
• [x] Foreman 3.11/Katello 4.13 (orcharhino 6.11 on EL8 only; orcharhino 7.0 on EL8+EL9; orcharhino 7.1 with Leapp)
• [x] Foreman 3.10/Katello 4.12
• [x] Foreman 3.9/Katello 4.11 (Satellite 6.15; orcharhino 6.8/6.9/6.10)
• [x] Foreman 3.8/Katello 4.10
• [x] Foreman 3.7/Katello 4.9 (Satellite 6.14)
• We do not accept PRs for Foreman older than 3.7.

[github-actions[bot]]

The PR preview for 138b1ac9b0e9b3d86f255052252a81dcbd18f264 is available at theforeman-foreman-documentation-preview-pr-3772.surge.sh

No diff compared to the current base

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[aneta-petrova]

Removing style review done because the PR has changed significantly since the original review.

[jherrman]

Apologies for the delay, I somehow forgot this PR is not closed yet. Will look into finishing it up ASAP.

[jherrman]

@aneta-petrova , if you can find a couple minutes, could you take one last look at the changes, so this could be merged? It's mostly about stylistic tweaks anyway, so hopefully shouldn't take too much effort.

[aneta-petrova]

Merged to "master", no cherry-picks necessary.

[aneta-petrova]

Don't take this too seriously, but this could be a required part of our onboarding process: to read all our guidelines, test them, and then suggest improvements :upside_down_face: