Explain the syntax of lists and dicts in the YAML chapter

[michmx]

In chapter 4, about YAML, lists and dicts are only illustrated without an explanation of the syntax.

Students must understand for example:

all members of a list are lines beginning at the same indentation level
starting with a "-" (a dash)
Space after the dash
etc.

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@michmx
I will add the following sentences:
Elements of a list start with a "- " (a dash and a space) at the same indentation level.
Elements of a dictionary are in the form of "key: value" (the colon must followed by a space)

[stale]

This issue or pull request has been automatically marked as stale because it has not had recent activity. Please manually close it, if it is no longer relevant, or ask for help or support to help getting it unstuck. Let me bring this to the attention of @klieret @wdconinc @michmx for now.