Add documentation for exit_tags

docs/strategy-advanced.md

@@ -143,6 +143,52 @@ def custom_sell(self, pair: str, trade: Trade, current_time: datetime, current_r
 !!! Note
     `buy_tag` is limited to 100 characters, remaining data will be truncated.
 
+## Exit tag
+
+Similar to [Buy Tagging](#buy-tag), you can also specify a sell tag.
+
+``` python
+def populate_sell_trend(self, dataframe: DataFrame, metadata: dict) -> DataFrame:
+    dataframe.loc[
+        (
+            (dataframe['rsi'] > 70) &
+            (dataframe['volume'] > 0)
+        ),
+        ['sell', 'exit_tag']] = (1, 'exit_rsi')
+
+    return dataframe
+```
+
+The provided exit-tag is then used as sell-reason - and shown as such in backtest results.
+
+!!! Note
+    `sell_reason` is limited to 100 characters, remaining data will be truncated.
+
+## Bot loop start callback
+
+A simple callback which is called once at the start of every bot throttling iteration.
+This can be used to perform calculations which are pair independent (apply to all pairs), loading of external data, etc.
+
+``` python
+import requests
+
+class AwesomeStrategy(IStrategy):
+
+    # ... populate_* methods
+
+    def bot_loop_start(self, **kwargs) -> None:
+        """
+        Called at the start of the bot iteration (one loop).
+        Might be used to perform pair-independent tasks
+        (e.g. gather some remote resource for comparison)
+        :param **kwargs: Ensure to keep this here so updates to this won't break your strategy.
+        """
+        if self.config['runmode'].value in ('live', 'dry_run'):
+            # Assign this to the class by using self.*
+            # can then be used by populate_* methods
+            self.remote_data = requests.get('https://some_remote_source.example.com')
+
+```
 
 ## Custom stoploss
 
@@ -501,32 +547,6 @@ class AwesomeStrategy(IStrategy):
 
 ---
 
-## Bot loop start callback
-
-A simple callback which is called once at the start of every bot throttling iteration.
-This can be used to perform calculations which are pair independent (apply to all pairs), loading of external data, etc.
-
-``` python
-import requests
-
-class AwesomeStrategy(IStrategy):
-
-    # ... populate_* methods
-
-    def bot_loop_start(self, **kwargs) -> None:
-        """
-        Called at the start of the bot iteration (one loop).
-        Might be used to perform pair-independent tasks
-        (e.g. gather some remote resource for comparison)
-        :param **kwargs: Ensure to keep this here so updates to this won't break your strategy.
-        """
-        if self.config['runmode'].value in ('live', 'dry_run'):
-            # Assign this to the class by using self.*
-            # can then be used by populate_* methods
-            self.remote_data = requests.get('https://some_remote_source.example.com')
-
-```
-
 ## Bot order confirmation
 
 ### Trade entry (buy order) confirmation