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.

dragonchain.go

@@ -2,47 +2,50 @@
 //
 // All API methods require a context.Context parameter for timeout and cancellation control.
 //
-// Example usage:
+// Example — fire and forget (most use cases):
 //
-//	package main
-//
-//	import (
-//	    "context"
-//	    "fmt"
-//	    "log"
-//	    "time"
-//
-//	    "git.dragonchain.com/dragonchain/prime-sdk-go"
-//	    "git.dragonchain.com/dragonchain/prime-sdk-go/models"
+//	client := sdk.NewDragonchainSDK(
+//	    "your-public-id",
+//	    "your-auth-key-id",
+//	    "your-auth-key",
+//	    "https://your-dragonchain-endpoint.com",
 //	)
 //
-//	func main() {
-//	    client := sdk.NewDragonchainSDK(
-//	        "your-public-id",
-//	        "your-auth-key-id",
-//	        "your-auth-key",
-//	        "https://your-dragonchain-endpoint.com",
-//	    )
+//	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+//	defer cancel()
 //
-//	    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.
 //
-//	    // Check system health
-//	    if err := client.System.Health(ctx); err != nil {
-//	        log.Fatal(err)
-//	    }
+// Example — wait for block inclusion (interchain / Daria):
 //
-//	    // Create a transaction
-//	    txn := &models.TransactionCreateRequest{
-//	        TxnType: "my-transaction-type",
-//	        Payload: map[string]interface{}{"message": "Hello Dragonchain"},
-//	    }
+//	resp, err := client.Transaction.Create(ctx, &models.TransactionCreateRequest{
+//	    TxnType: "my-transaction-type",
+//	    Payload: `{"message": "Hello Dragonchain"}`,
+//	})
+//	if err != nil {
+//	    log.Fatal(err)
+//	}
 //
-//	    resp, err := client.Transaction.Create(ctx, txn)
+//	// 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)
 //	    }
-//	    fmt.Printf("Created transaction: %s\n", resp.TransactionID)
+//	    if txn.Header.BlockId != "" {
+//	        fmt.Printf("Block ID: %s\n", txn.Header.BlockId)
+//	        break
+//	    }
 //	}
 package sdk