Add docs on ability to create transfer from two existing transactions (#321)

Docs for PR https://github.com/actualbudget/actual/pull/2398+

as part of the feature
https://github.com/actualbudget/actual/issues/1891+

docs/transactions/transfers.md

@@ -4,15 +4,39 @@ If you want to transfer money between accounts, you want to do it in a way that
 
 When you create a transfer in Actual, those two transactions are linked and updating one always automatically updates the other. For example, if you typed something into the **Notes** column it would appear in both transactions.
 
+![](/img/transfers/transfer-complete.png)
+
 ## Creating a transfer
 
 In the **Payee** field of a transaction, choose the account in the dropdown you want to transfer to/from. You can press **Make Transfer** if you want to just see a list of accounts and hide other payees.
 
+![](/img/transfers/payees-dropdown.png)
+
 :::caution
 A transaction in the corresponding account will automatically be created.
 :::
 
-If you are importing files, it is recommended to import into a single account and create the transfer first, and then import the second account. This way the transaction in the second account is automatically reconciled to the transfer transaction. If you imported to both accounts first, creating the transfer would create a duplicate transaction.
+If you are importing files, it is recommended to import into a single account and create the transfer first, and then import the second account. This way the transaction in the second account is automatically reconciled to the transfer transaction. If you imported to both accounts first, you can [make a transfer from the already imported transactions](#make-a-transfer-from-two-existing-transactions).
+
+### Make a transfer from two existing transactions
+
+:::note
+This process will only apply when the below conditions are met
+
+- The two transactions are related to different accounts
+- The amounts are exactly the same but inverted e.g. a **debit** of `1.00` and a **credit** of `1.00`
+- The transaction is not part of a split transaction.
+
+:::
+
+Make a transfer of existing transactions in the same way you [bulk-edit transactions](bulk-editing.md).
+
+![](/img/transfers/make-transfer-tooltip.png)
+
+1. Go to a multi-account view like “All accounts” so that you can see all transactions.
+2. Identify the transactions that you wish to change and select the tick box in the left hand column (by the date column).
+3. Go to the drop down top right (the arrow below “2 transactions”)
+4. If the transactions are valid to be converted to a transfer, you can click **Make transfer**.
 
 ## Deleting a transfer