fix bash completion install command

[a-fleming]

Summary

Fixes the Linux bash completion install example in the generated Cobra help text.

The previous command used shell redirection directly into /etc/bash_completion.d/bootdev, which usually fails for non-root users:

bootdev completion bash > /etc/bash_completion.d/bootdev

The updated command uses sudo tee so only the file write is elevated:

bootdev completion bash | sudo tee /etc/bash_completion.d/bootdev > /dev/null

Testing

Ran:

go test ./...
go run . help completion bash

go test ./... passes. Verified that the Linux bash completion example now uses sudo tee.