Fix getting started guide filename

[redeux]

Description

This is a very simple PR that fixes a filename error in the documentation which prevents the Getting Started guide from displaying when the link is followed from README.md

Acceptance tests

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Output from acceptance testing:

Release Note

Release note for CHANGELOG:

NONE

References

closes #2685

Community Note

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[hashicorp-cla-app]

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Phil Sautter seems not to be a GitHub user.
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[redeux]

It seems like there's a problem with my old CLA. It shows that I signed it but it's not picked up from GH. Feel free to close this and make the change as appropriate.

Thanks!