add gotcha

Author: lrvideckis

library/graphs/bridges_cuts/bcc_callback.hpp

@@ -6,7 +6,7 @@
 //!     vector<pii> edges(m);
 //!     UF uf(n);
 //!     bcc_callback(adj, [&](const vi& nodes) {
-//!       if (sz(nodes) > 2)
+//!       if (sz(nodes) > 2) // assumes no multiple edges
 //!         for (int v : nodes) uf.join(v, nodes[0]);
 //!     });
 //!     vector<basic_string<int>> bridge_tree(n);