TOOL-31618 Add a repo-side testing doc to linux-pkg for the bugfix pipeline

CLAUDE.md

@@ -0,0 +1,14 @@
+# Conventions for Claude Code in this repo
+
+## Testing a change
+
+See [docs/testing.md](docs/testing.md) — how to test a change to `linux-pkg` itself, how CI for a
+package works, and how to use `linux-pkg` to build/validate a change made in one of the many
+packages it orchestrates.
+
+## Keeping this file and docs/testing.md current
+
+A change to a tool, option, mode, job, or package list — or a newly found (or fixed) gotcha —
+should update `docs/testing.md`. If this repo ever gains a second AI-agent instruction file (e.g.
+`.github/copilot-instructions.md`, which does not exist today), carry this same testing-doc
+pointer into it too; nothing keeps two such files in sync automatically.

README.md

@@ -877,6 +877,11 @@ is to create an official repository for it.
 
 ## Testing your changes
 
+For a reader that will act on this programmatically — exact commands, preconditions, pass/fail
+signals, and how `linux-pkg` is used to build/validate a change made in one of its orchestrated
+packages — see [docs/testing.md](docs/testing.md), which expands on this section rather than
+duplicating it.
+
 ### Testing changes to an existing package
 
 If you are not making any changes to linux-pkg, only changes to a given