Update documentation for forcebuy query

docs/telegram-usage.md

@@ -243,10 +243,14 @@ Return a summary of your profit/loss and performance.
 
 > **BITTREX:** Selling BTC/LTC with limit `0.01650000 (profit: ~-4.07%, -0.00008168)`
 
-### /forcebuy <pair>
+### /forcebuy <pair> [rate]
 
 > **BITTREX:** Buying ETH/BTC with limit `0.03400000` (`1.000000 ETH`, `225.290 USD`)
 
+Omitting the pair will open a query asking for the pair to buy (based on the current whitelist).
+
+![Telegram force-buy screenshot](assets/telegram_forcebuy.png)
+
 Note that for this to work, `forcebuy_enable` needs to be set to true.
 
 [More details](configuration.md#understand-forcebuy_enable)
@@ -254,6 +258,7 @@ Note that for this to work, `forcebuy_enable` needs to be set to true.
 ### /performance
 
 Return the performance of each crypto-currency the bot has sold.
+
 > Performance:  
 > 1. `RCN/BTC 57.77%`  
 > 2. `PAY/BTC 56.91%`  

tests/rpc/test_rpc_telegram.py

@@ -930,6 +930,11 @@ def test_forcebuy_no_pair(default_conf, update, mocker) -> None:
     assert inline_msg_mock.call_args_list[0][1]['callback_query_handler'] == 'forcebuy'
     keyboard = inline_msg_mock.call_args_list[0][1]['keyboard']
     assert reduce(lambda acc, x: acc + len(x), keyboard, 0) == 4
+    update = MagicMock()
+    update.callback_query = MagicMock()
+    update.callback_query.data = 'XRP/USDT'
+    telegram._forcebuy_inline(update, None)
+    assert fbuy_mock.call_count == 1
 
 
 def test_performance_handle(default_conf, update, ticker, fee,