Some minor documentation additions

[merriam]

I have only used Textual for a about a week, and would like to make a few documentation additions:

1. Mention more source examples. Expand the Example Code paragraph on the first page of the guide to mention the doc/examples trees, and the specific directories in the beginning of the Widgets, Containers, and Actions pages.
2. Fix minor typos as I run across them again.
3. Add two sentences to Visibility and Display pages explaining how they are different, and that they take different parameters.
4. Add noters to Label and Static explaining they are similar outside of CSS styling.
5. Add better explanation of datafile's sort, clarifying what exactly is sent in the column parameters.
6. Mention how DataTables move_row(1) gives a starting cursor and that row numbers start at 1.
7. Mention that there is currently no filter() style functionality; it is often searched for.
8. Mention or add an example where a table is quickly displayed without a cursor (show_cursor(False)) for a simple reactive display.
9. Mention DataTable meaning of "selected" and "highlighted" records.
10. Clarify various zebra-stripes references to talk about .datatable--even-row style.
11. Add a FAQ section about debugging Textual Apps with PyCharm and Visual Studio.

My thought is to just write up what I can, each section as a separate commit in a PR, and submit. Any thoughts?

[github-actions]

We found the following entry in the FAQ which you may find helpful:

• How do I pass arguments to an app?

Feel free to close this issue if you found an answer in the FAQ. Otherwise, please give us a little time to review.

This is an automated reply, generated by FAQtory

[merriam]

Seriously, has anyone ever closed an issue from FAQtory? Ever?

[davep]

Seriously, has anyone ever closed an issue from FAQtory? Ever?

Yeah, a few times actually.