Add documentation about tricky runtime method search

src/app/components/RuntimeTransactionMethod/index.tsx

@@ -149,10 +149,31 @@ export const getRuntimeTransactionMethodFilteringParam = (
     case 'any':
       return {}
     case 'accounts.Transfer':
+      // Searching for transfers is tricky, because there are some
+      // transactions which are in fact evm.Calls, but are still
+      // considered to be transfers based on some heuristics.
+      // The Nexus API provides a special value in order to allow searching
+      // for them. Their documentation says:
+      //
+      // 'native_transfers': Returns transactions "likely to be native transfers".
+      // These include accounts.Transfer transactions and evm.Calls with an empty 'body' field.
+      //
+      // For more details, see the API spec at
+      // https://github.com/oasisprotocol/nexus/blob/main/api/spec/v1.yaml
       return { method: 'native_transfers' }
     case 'evm.Call':
+      // Searching for contract calls is tricky, because some of them
+      // should be classified as transfers. (See above.)
+      // The Nexus API provides a special value for excluding these
+      // from the search. Their documentation says:
+      //
+      // 'evm.Call_no_native': Returns EVM calls that are "not likely to be native transfers".
+      //
+      // For more details, see the API spec at
+      // https://github.com/oasisprotocol/nexus/blob/main/api/spec/v1.yaml
       return { method: 'evm.Call_no_native' }
     default:
+      // For other (normal) methods, we can simply pass on the wanted method name.
       return { method }
   }
 }