add note about selection sets in serial execution examples

[thomasheyenbrock]

The examples for serial execution in the section Normal and Serial Execution actually use a query as operation type. This PR proposes to change these examples to mutations (which are actually required to be executed serially).

I also added in the variables in the first of these examples for the operation to be valid.

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[benjie]

Thanks for submitting a suggestion 🙌

The spec text here states (emphasis mine):

For example, given the following selection set to be executed serially:

The examples are not GraphQL documents, they are selection sets, your edits turn them into documents but that change is not desired.

[thomasheyenbrock]

Aaah, got it 👍 Though it's easy to read over that and there's a bit of ambiguity here in the sense that one can't tell the difference from a selection set to a document using the query shorthand. What do you think about adding a note here to clear this up?

[benjie]

What do you think about adding a note here to clear this up?

Let's see what you have in mind 👍

[thomasheyenbrock]

Updated the PR description and replaced the commit with a new one that just adds a note 🙂

[benjie]

I'm not convinced this is necessary given the text above the example explicitly states selection set, but I'll let others comment 👍