Indent our admonitions a bit more

[choldgraf]

I noticed that many other nice-looking documentation sites have an obvious indentation level between their admonition text and the text in the rest of the document.

e.g.:

netlify:

metaflow:

And a comparison from the sphinx-book-theme for example:

This makes me think two things:

1. We don't have as much whitespace in general in our admonitions
2. The admonition text feels like it "flows" with the main text in our case because of the lack of indentation

Do others think it would be useful to try adding a bit more whitespace to admonition blocks, and in particular on the left margin?

[jorisvandenbossche]

Yes, I had the same "first impression" when seeing the admonitioins in the actual pandas docs. We should probably add a bit more margin around the text in the admonitions. Fully agreed!

I think there can be more whitespace in all margins, not only the left

[choldgraf]

What about something like:

[jorisvandenbossche]

Looks much better I think!

I would personally still do a little bit more vertical space at the bottom as well.

[choldgraf]

see #207