chore: add withPgClient import in docs

[MarioSimou]

Description

Update withPgClient example to include the necessary imports.

Performance impact

None

Security impact

None

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

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Latest commit: f5d2ddd

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[benjie]

Thanks! Since this is in the grafast.org website it can't refer to the postgraphile/@dataplan/pg import (Grafast doesn't "know" about PostGraphile), but you should definitely use the postgraphile/@dataplan/pg path in your own projects to avoid duplicate module issues. You can also access it from build.dataplanPg.withPgClient which is the preferred way.