clarify XLS-0102 host function stability rule (#7146)

src/libxrpl/tx/wasm/WasmVM.cpp

@@ -13,7 +13,13 @@
 #include <memory>
 
 namespace xrpl {
-
+// WARNING: Per XLS-0102, the host functions registered here form a stable
+// ABI. Their name, semantics, parameters, and return types must NEVER be
+// changed, as there may always be a program that uses it. New host functions
+// may be added and existing gas costs may be adjusted, but every such change
+// must be gated by an amendment.
+// See XLS-0102 §6.5 (Future-Proofing):
+// https://github.com/XRPLF/XRPL-Standards/tree/master/XLS-0102-wasm-vm#65-future-proofing
 static void
 setCommonHostFunctions(HostFunctions* hfs, ImportVec& i)
 {