Doc comments

• Page getting started / Standalone query operators: "The example from the previous section can also be ..." . Where does this refer to? The previous page has no example, it is the intro page.
• A suggestion for the page "Gettinge started" : it should have a section that actually defines what _ and {} mean ? Introduction, Getting Started and not even Standalone Query commands seem to define them. Of course I know that _ is supposed to stand for the "current named tuple" but maybe it is good to have a quick paragraph defining these concepts?
• Page Data sources / Any iterable type : The page uses start, next, done which are invalid. Is the paragraph in general correct? I remember from the workshop that anything that behaves as an iterator of NamedTuples can be a data source.

Start with the Getting Started, Standalone query operators, and Data sources / Any iterable type pages named in the issue. Check the previous-section reference, define _ and {}, and verify the iterator terminology against the documented data-source behavior. Done means the affected text is accurate, clear, and internally consistent.