Implement previous backtest result reuse when config and strategy did not change.

docs/backtesting.md

@@ -76,6 +76,7 @@ optional arguments:
                         _today.json`
   --breakdown {day,week,month} [{day,week,month} ...]
                         Show backtesting breakdown per [day, week, month].
+  --no-cache            Do not reuse cached backtest results.
 
 Common arguments:
   -v, --verbose         Verbose mode (-vv for more, -vvv to get all messages).
@@ -457,6 +458,10 @@ freqtrade backtesting --strategy MyAwesomeStrategy --breakdown day month
 
 The output will show a table containing the realized absolute Profit (in stake currency) for the given timeperiod, as well as wins, draws and losses that materialized (closed) on this day.
 
+### Backtest result caching
+
+To save time, by default backtest will reuse a cached result when backtested strategy and config match that of previous backtest. To force a new backtest despite existing result for identical run specify `--no-cache` parameter.
+
 ### Further backtest-result analysis
 
 To further analyze your backtest results, you can [export the trades](#exporting-trades-to-file).