README npm install section mentions Python and C/C++ but they are no longer needed

The README's [npm install section](https://github.com/devcontainers/cli/blob/v0.86.0/README.md?plain=1#L59) says:

> To install the npm package you will need Python and C/C++ installed to build one of the dependencies (see, e.g., [here](https://github.com/microsoft/vscode/wiki/How-to-Contribute) for instructions).

This hasn't been true since v0.50.0. PR #585 removed `node-pty` from the published package, and `build/patch-packagejson.js` strips all `dependencies` before `npm pack`, so the tarball on npm has no deps to install at all.

Quick check with `node:24-slim`, which has no build toolchain:

```
$ docker run --rm node:24-slim sh -c "which python3 || echo 'not found'; which gcc || echo 'not found'; which make || echo 'not found'"
not found
not found
not found

$ docker run --rm node:24-slim sh -c "npm install -g @devcontainers/cli 2>&1 && npm list -g && devcontainer --version"
added 1 package in 1s
/usr/local/lib
+-- @devcontainers/cli@0.86.0
+-- corepack@0.34.6
`-- npm@11.11.0

0.86.0
```

Installs and runs fine without any build toolchain.

The prerequisite note and the link to the VS Code "How to Contribute" wiki should be removed from this section.

## Related

- #63
- #585