Make Copilot aware of the instruction-architecture doc when editing instruction and agent files (#62377)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 8fa5a1bb-46b5-4ceb-8219-795bf8209e1f

Author: lecoursen

.github/instructions/instruction-architecture.instructions.md

@@ -0,0 +1,13 @@
+---
+applyTo: ".github/instructions/**,.github/agents/**"
+---
+
+# Editing Copilot content instruction and agent files
+
+This applies when you add, edit, or remove a Copilot instruction or shared agent file that guides how **content** (articles, data files) is written. It does **not** apply to code instructions or agents owned by the engineering team (for example `code.instructions.md`).
+
+When it applies, you **must** first read the instruction-architecture doc in full and follow it:
+
+https://github.com/github/docs-team/blob/main/contributing-to-docs/docs-work/copilot-instruction-architecture.md
+
+Read the current version every time (from a local `github/docs-team` checkout if you have one, otherwise fetch the URL); do not rely on your memory of it, because it changes. If you cannot access it, say so and stop rather than guessing.