Update index.mdx

[bmeyer99]

Description

What does this PR do?
Adds language how to install CLI

TODO only if you're a HashiCorp employee

• Backport Labels: If this fix needs to be backported, use the appropriate backport/ label that matches the desired release branch. Note that in the CE repo, the latest release branch will look like backport/x.x.x, but older release branches will be backport/ent/x.x.x+ent.
  • LTS: If this fixes a critical security vulnerability or severity 1 bug, it will also need to be backported to the current LTS versions of Vault. To ensure this, use all available enterprise labels.
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
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  in the PR description, commit message, or branch name.
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[Copilot]

Pull Request Overview

This PR updates the Vault CLI documentation by adding an installation instruction to index.mdx.

• Adds a new humorous installation message for the Vault CLI.

[Copilot]

[nitpick] The tone of the installation instruction is humorous, which may not be appropriate for documentation targeting a professional audience. Consider rewriting the statement in a clearer and more professional manner by providing concise and actionable installation steps.