Add authoritative sources requirement to AGENTS.md

Author: s-celles

AGENTS.md

@@ -9,4 +9,5 @@
 - create GitHub issues for follow-up work discovered during implementation
 - ask clarifying questions when requirements are ambiguous rather than making assumptions
 - ensure that content have disclamer about ai assistance usage, that some agents, skills and commands are experimental (ie untested)
-- ensure that internal url points to https://s-celles.github.io/ai-config/
+- ensure that internal url points to https://s-celles.github.io/ai-config/
+- use authoritative sources (official documentation, standards bodies, .gov/.edu sites, peer-reviewed publications) and cite them with links