Enable easier custom MetaHuman use

[Krxtopher]

Issue:

https://github.com/aws-samples/amazon-polly-metahumans/issues/6

Description of changes:

The previous Content folder organization made it very difficult to successfully incorporate new MetaHumans into this sample project. This resulted in a number of users reporting issues. This PR addresses these problems in two ways:

1) The Content folder has been reorganized to better accommodate custom MetaHuman import. 2) The "Developer Guide" has been updated with more detailed instructions on how to import and use custom MetaHumans.

Additionally, this PR fixes an error in one of the documentation images.

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[Krxtopher]

sometimes there is some quirkiness with moving files into different folders, did you move these assets using UE or did you move them using like the OS file explorer?

The safe way to reorganize content files in UE is to follow this process...

• Move the files using the Editor's Content Browser.
• Once all moves are complete, right click on the top level folder in the Content Browser and choose "Fix Up Redirectors in Folder". This rewrites all asset dependency references so that they are pointing directly to the new location of the moved assets (instead of using soft, re-routing links).
• If needed, again using the Content Browser, delete any "empty" folders that got left behind. (This can happen if a folder contained nothing but invisible redirectors.)

Also - did you verify the play execution works after the change?

Yes. I verified that our standard demo map worked and also verified that I could import and a custom MetaHuman and get it working.