Update tekton example README and file names

[Megan-Wright]

For: #53

• Restructures the files so they can be applied to a cluster more easily
• Renames some files to be more readable
• Updates readme to reflect file structure changes and simplify

[a-roberts]

Thanks @Megan-Wright, I'll take a look at this one and try it 😄

And then let's do a follow-up for tkn, I see tektoncd/cli#940 is being worked so that's a good find

[a-roberts]

Added what I've picked up on the docs so far, giving this a try now (and in fairness to @Megan-Wright I know the text was already here, but now's a good time to clean things up and make it easier to understand)

[CarolynMabbott]

I'll have a look too

[a-roberts]

Much better, thanks Megan, I noticed the example pipeline here is doing a Docker build and the example repositories we reference aren't of the gitops structure we'd like (i.e. those in the main readme), happy to address as a follow-up issue though. After this morning's tests I think we're almost there.

For the last section on the promote run - so I need a third repository then? Update: I do, that TaskRun worked fine, let's update that and address any follow-ups separately.