loop: emphasize directory guidance

Make it clearer and more emphatic that agents must check and read
directory-specific guidance files before making changes to files.

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: s624b7b2b4c7c1054k
diff --git a/loop/donetool.go b/loop/donetool.go
index 12db3b8..a5d6d72 100644
--- a/loop/donetool.go
+++ b/loop/donetool.go
@@ -54,6 +54,10 @@
       "type": "object",
       "description": "Collection of checklist items",
       "properties": {
+        "checked_guidance": {
+          "$ref": "#/definitions/checklistItem",
+          "description": "I checked for and followed any directory-specific guidance files for all modified files."
+        },
         "wrote_tests": {
           "$ref": "#/definitions/checklistItem",
           "description": "If code was changed, tests were written or updated."