Update instructions and test case description

[alexmitchelldev]

Resolves #1818

Updated instructions.md to be less 'technical' and feel more part of the story. I also updated the test case description for the orderFromGrocer function to properly reflect the function name and arguments passed.

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[SleeplessByte]

(Have not forgotten about this! I'll try to go through this this week <3)

[alexmitchelldev]

@SleeplessByte did you ever get chance to take a look at this?

[SleeplessByte]

@alexmitchelldev apologies. Short explanation at the end of this post https://forum.exercism.org/t/issue-with-local-jest-type-definitions-yarn-3-and-jest/6867/24

@ErikSchierboom @junedev @tejasbubane any of you time to check this?

[alexmitchelldev]

@ErikSchierboom sorry about the glacial response time. I have committed your suggestions.

[ErikSchierboom]

Thanks!