docs(readme): broaden policy editor role to SME or engineering lead

EM is too narrow — in practice the person who owns the policy doc
is whoever has subject-matter authority, which might be a staff
engineer, a tech lead, or a domain SME, not always a people manager.

Author: Srikanth-AD

README.md

@@ -131,7 +131,7 @@ modification produces a hash mismatch and stackguard refuses to run
 until the team's official hash is updated.
 
 This makes policy updates a deliberate, reviewable act:
-1. Engineering manager edits the policy
+1. SME or engineering lead edits the policy
 2. Runs `stackguard policy hash`
 3. Updates `policyHash` in `stackguard.json`
 4. Both changes go through PR review together