devguides: add subtract_fee_from_outputs to wallet-rpc transfer

resources/developer-guides/wallet-rpc.md

@@ -687,6 +687,7 @@ Inputs:
   * *address* - string; Destination public address.
 * *account_index* - unsigned int; (Optional) Transfer from this account index. (Defaults to 0)
 * *subaddr_indices* - array of unsigned int; (Optional) Transfer from this set of subaddresses. (Defaults to empty - all indices)
+* *subtract_fee_from_outputs* - array of unsigned int; (Optional) Choose which destinations to fund the tx fee from instead of the change output. The fee will be subtracted evenly from each destination (regardless of amount). Do not use this if recipient requires an exact amount.
 * *priority* - unsigned int; Set a priority for the transaction. Accepted Values are: 0-3 for: default, unimportant, normal, elevated, priority.
 * *mixin* - unsigned int; Number of outputs from the blockchain to mix with (0 means no mixing).
 * *ring_size* - unsigned int; Number of outputs to mix in the transaction (this output + N decoys from the blockchain). (Unless dealing with pre rct outputs, this field is ignored on mainnet).
@@ -728,6 +729,32 @@ $ curl http://127.0.0.1:18082/json_rpc -d '{"jsonrpc":"2.0","id":"0","method":"t
 }
 ```
 
+In the example below, we use `subtract_fee_from_outputs` to deduct the transaction fee from the 1st and 2nd destinations. 
+
+```
+$ curl http://127.0.0.1:18082/json_rpc -d '{"jsonrpc":"2.0","id":"0","method":"transfer","params":{"destinations":[{"amount":10000000000,"address":"5AVBTfFcsVjfxN4VqGqykY69M2bDd6a8F6ZMt27qFbAHJX6VKzkcH5XW9d6VGQVk7mD4H11q6GDeA3v8aRdzGZrnBqdMxpB"},{"amount":30000000000,"address":"73a4nWuvkYoYoksGurDjKZQcZkmaxLaKbbeiKzHnMmqKivrCzq5Q2JtJG1UZNZFqLPbQ3MiXCk2Q5bdwdUNSr7X9QrPubkn"}],"subtract_fee_from_outputs":[0,1]}}' -H 'Content-Type: application/json'
+{
+  "id": "0",
+  "jsonrpc": "2.0",
+  "result": {
+    "amount": 39824160000,
+    "amounts_by_dest": {
+      "amounts": [9912080000,29912080000]
+    },
+    "fee": 175840000,
+    "multisig_txset": "",
+    "spent_key_images": {
+      "key_images": ["f37c0a375f09c0098d8320496fd74f387bc0992faebaae85be87f4431f66fcc1","7356f719e6537e39f2bf1f1c7088c8d1b76b3b62a30b19a564b9d3e1deb3b0f3"]
+    },
+    "tx_blob": "",
+    "tx_hash": "27d3821ab89b001b24de2e9468d032820a64752afe929c8cfeb084f28fb30dd3",
+    "tx_key": "",
+    "tx_metadata": "",
+    "unsigned_txset": "",
+    "weight": 2791
+  }
+
+```
 
 ### **transfer_split**