Document fire-and-forget transaction mode

Add godoc to Create and CreateBulk explaining they return immediately
without waiting for block inclusion. Update package-level example to show
both fire-and-forget and wait-for-block patterns. Add Transaction Modes
section to README with code examples.

README.md

@@ -65,6 +65,57 @@ func main() {
 }
 ```
 
+## Transaction Modes
+
+`Create` and `CreateBulk` return **immediately** with the assigned transaction ID(s). They do **not** wait for block inclusion. Blocks are assembled asynchronously on a ~5-second cycle.
+
+### Fire and Forget
+
+Most use cases only need the transaction ID. No polling required.
+
+```go
+ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+defer cancel()
+
+resp, err := client.Transaction.Create(ctx, &models.TransactionCreateRequest{
+    TxnType: "my-transaction-type",
+    Payload: `{"message": "Hello Dragonchain"}`,
+})
+if err != nil {
+    log.Fatal(err)
+}
+fmt.Printf("Transaction ID: %s\n", resp.TransactionID)
+// Done — no need to wait for a block.
+```
+
+### Wait for Block
+
+If you need the block ID (e.g. for interchain verification or Daria), poll `Get` until `Header.BlockId` is populated.
+
+```go
+resp, err := client.Transaction.Create(ctx, &models.TransactionCreateRequest{
+    TxnType: "my-transaction-type",
+    Payload: `{"message": "Hello Dragonchain"}`,
+})
+if err != nil {
+    log.Fatal(err)
+}
+
+// Poll until the transaction is included in a block.
+ticker := time.NewTicker(2 * time.Second)
+defer ticker.Stop()
+for range ticker.C {
+    txn, err := client.Transaction.Get(ctx, resp.TransactionID)
+    if err != nil {
+        log.Fatal(err)
+    }
+    if txn.Header.BlockId != "" {
+        fmt.Printf("Block ID: %s\n", txn.Header.BlockId)
+        break
+    }
+}
+```
+
 ## Available Endpoints
 
 All API methods accept a `context.Context` as their first parameter for timeout and cancellation control.