add md version of non-Nebari helpers

[amsnyder]

Fix for execution issue mentioned in #286.

I didn't make these md files appear executed, but I think that's probably fine for these notebooks.

[gzt5142]

We should talk about naming before committing this.

Here's why:

• Recall that the file names in the TOC lack extensions (.md, .ipynb, etc).
• This is meant to be a feature, not a bug
• If the compiler finds two files with the same base name but different extensions, it will be forced to pick which one you want in the book.
• It may not pick right.

When building, the compiler will warn that it found two filenames of the same root name with different prefix. To avoid the warning and to ensure that the correct file gets compiled, the basename should be different.

In my opinion, we could easily hide these in a sub-folder (and keep the names they have) to both avoid this compiler problem and to reduce the confusion in the repo.

[amsnyder]

I've pushed them into a sub-folder! Let me know if you think this is ready to merge - or we can wait until we talk on Monday if you want to discuss the formatting.

[gzt5142]

Good News....

I was mistaken when I said there was not a way to force a notebook into the book without executing it. I have a way to do that now that I didn't know before.... It involves touching the _config.yml (in addition to the _toc.yml), but we wouldn't have to make these ghost documents.