Improve installation guide for Linux

[JoergStrebel]

Describe the feature or problem you'd like to solve

Improve Copilot installation instructions for Linux

Proposed solution

The problem is that Linux is installed using distributions (e.g. OpenSUSE Leap). These distributions bring their own npm packages. I tried to install copilot after installing the npm package from my distribution and the copilot install command failed with an EACCES error. The necessary nodejs code could not be installed globally on my machine without root permissions. (see https://docs.npmjs.com/resolving-eacces-permissions-errors-when-installing-packages-globally/)
Copilot installation only worked after I deleted the npm distribution package, and used nvm to install node (see https://docs.npmjs.com/downloading-and-installing-node-js-and-npm/ and https://github.com/nvm-sh/nvm)
Maybe you could point this out in a README or so.

Example prompts or workflows

npm install -g @github/copilot won't work with npm installed using your Linux package manager.

Additional context

No response

[EvanBoyle]

Thank you for the report, and glad you were able to get it installed. Longer term the fix here will be to enable users to install the CLI via native packages managers, but that requires some work to build a single binary that doesn't rely on the system version of node: #16