docs(Shell-Completion.md): modified conditional for .zshrc to include…

[kreig303]

… call to compinit

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
  n/a Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

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cf. #7059 for a complete description.

Essentially need to add two lines to the if fi statement for adding to the .zshrc to ensure compinit is loaded and available.

[MikeMcQuaid]

Makes sense to me!
Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @kreig303!

[kreig303]

nw @MikeMcQuaid

i know it's not a major change but there's a fixed overhead to each & every issue+pr so hth!