docs: consolidate getting started guides (PROJQUAY-2500)

[flavianmissi]

We have a few different "Getting started" guides, which can confuse a newcomer (it did confuse me x)).
This PR merges a couple guides, and renames another - hopefully stopping any potential confusion.

[app-sre-bot]

Can one of the admins verify this patch?

[bcaton85]

LGTM

[flavianmissi]

/cherry-pick redhat-3.6

[openshift-cherrypick-robot]

@flavianmissi: #884 failed to apply on top of branch "redhat-3.6":

Applying: docs: consolidate getting started guides (PROJQUAY-2500)
Using index info to reconstruct a base tree...
M	README.md
M	docs/docker-local-dev.md
Falling back to patching base and 3-way merge...
CONFLICT (modify/delete): docs/docker-local-dev.md deleted in docs: consolidate getting started guides (PROJQUAY-2500) and modified in HEAD. Version HEAD of docs/docker-local-dev.md left in tree.
Removing docs/development-container.md
Auto-merging README.md
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0001 docs: consolidate getting started guides (PROJQUAY-2500)
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick redhat-3.6

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