doc/testnet/payment: add screenshots and minor edit

doc/src/testnet/payment.md

@@ -1,14 +1,16 @@
 # Payments
 
 Using the tokens we minted, we can make payments to other addresses.
-Let's try to send some `WCKD`
+Let's try to send some `MLDY`
 tokens to `8sRwB7AwBTKEkyTW6oMyRoJWZhJwtqGTf7nyHwuJ74pj`:
 
 ```
-$ ./drk transfer 2.69 WCKD \
+$ ./drk transfer 2.69 MLDY \
     8sRwB7AwBTKEkyTW6oMyRoJWZhJwtqGTf7nyHwuJ74pj > payment_tx
 ```
 
+![transfer](img/transfer.png)
+
 The above command will create a transfer transaction and place it into
 the file called `payment_tx`. Then we can broadcast this transaction
 to the network:
@@ -17,6 +19,8 @@ to the network:
 $ ./drk broadcast < payment_tx
 ```
 
+![transfer](img/broadcast-transfer.png)
+
 On success we'll see a transaction ID. Now again the same confirmation
 process has to occur and `8sRwB7AwBTKEkyTW6oMyRoJWZhJwtqGTf7nyHwuJ74pj`
 will receive the tokens you've sent.
@@ -28,6 +32,7 @@ We can see the spent coin in our wallet.
 ```
 $ ./drk wallet --coins
 ```
+![coins](img/spent-coins.png)
 
 We have to wait until the next block to see our change balance reappear
 in our wallet.
@@ -36,3 +41,5 @@ in our wallet.
 $ ./drk wallet --balance
 ```
 
+![all-balances](img/all-balances.png)
+