docs: header comment now matches python -m pip install convention

The rest of the tree (README, install.ts, sample-workflow README,
welcome panel) moved to `python -m pip install` for the v1.0.1 batch;
extension.ts's file header still pointed users at the bare `pip install`
form. Trivially confusing for anyone reading the top of the file.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dmartinochoa

src/extension.ts

@@ -8,7 +8,7 @@
 // position translation).
 //
 // The server itself lives upstream in `dmartinochoa/pipeline-check`
-// under `pipeline_check/lsp/`; install via `pip install
+// under `pipeline_check/lsp/`; install via `python -m pip install
 // "pipeline-check[lsp]"`.
 
 import * as vscode from "vscode";