Documentation fix typo "an MacOS" to "on MacOS"

[FlogFr]

Pull Request

I am discovering this amazing project ! Thank you very much for it.
During reading the documentation I found this typo. I open this PR to fix it.

What? (description)

Documentation typo.

Why? (reasoning)

Acceptance

Please use the following checklist:

• you linked an issue (if applicable)
• you included tests (if applicable)
• you ran conformance (make conformance)
• you formatted your code (make fmt)
• you linted your code (make lint)
• you generated documentation (make docs) . make docs fail on the following error :

7.750 2025/01/20 19:48:49 generating docs for type: "KernelModuleConfig"
------
Dockerfile:355
--------------------
 353 |     RUN gofumpt -w ./pkg/
 354 |     WORKDIR /src/pkg/machinery
 355 | >>> RUN --mount=type=cache,target=/.cache go generate ./...
 356 |     RUN gotagsrewrite .
 357 |     RUN goimports -w -local github.com/siderolabs/talos ./
--------------------
ERROR: failed to solve: process "/toolchain/bin/bash -c go generate ./..." did not complete successfully: exit code: 1

• you ran unit-tests (make unit-tests)

See make help for a description of the available targets.

[smira]

thank you!

[smira]

/m