Document how to update Copilot CLI on the install page

[kaviraj07]

Code of Conduct

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What article on docs.github.com is affected?

https://docs.github.com/en/copilot/how-tos/copilot-cli/set-up-copilot-cli/install-copilot-cli

What part(s) of the article would you like to see updated?

The "Installing Copilot CLI" article documents how to install the CLI across all supported package managers (npm, WinGet, Homebrew, install script, direct download), but it doesn't mention how users keep the CLI up to date after installation.

The /update slash command and the copilot update shell command are both documented in the CLI command reference (https://docs.github.com/en/copilot/reference/copilot-cli-reference/cli-command-reference), but users landing on the install/setup page have no signal that these options exist. They may assume they need to rerun their original install command (npm install -g, brew upgrade, winget upgrade, etc.) to get the latest version.

Suggested change: Add a short "Updating Copilot CLI" section to the install page that mentions both update methods and links to the canonical command reference for the full list of commands.

Expected outcome: Users setting up the CLI discover the in-place update commands in the same place they learned to install it, without having to navigate to a separate reference doc.

Additional information

Linked PR #44460

[Juma-creator]

Updating Copilot CLI

To update to the latest version:

• Run copilot update in your terminal, or
• Use the /update slash command in Copilot Chat.
  See the full command list in the CLI reference.