reword unseen, missing and ignore format (#609)

* update unseen and ignore format docstrings

* update missing values docstrings

Author: solegalli

feature_engine/_docstrings/init_parameters/all_trasnformers.py

@@ -17,8 +17,8 @@
     """.rstrip()
 
 _missing_values_docstring = """missing_values: string, default='raise'
-        Indicates if missing values should be ignored or raised. If 'raise' the
+        Indicates if missing values should be ignored or raised. If `'raise'` the
         transformer will return an error if the the datasets to `fit` or `transform`
-        contain missing values. If 'ignore', missing data will be ignored when learning
-        parameters or performing the transformation.
+        contain missing values. If `'ignore'`, missing data will be ignored when
+        learning parameters or performing the transformation.
         """.rstrip()

feature_engine/_docstrings/init_parameters/encoders.py

@@ -2,14 +2,17 @@
         This transformer operates only on variables of type object or categorical. To
         override this behaviour and allow the transformer to transform numerical
         variables as well, set to `True`.\n
-        If `ignore_format` is False, the encoder will automatically select variables of
-        type object or categorical, or check that the variables entered by the user are
-        of type object or categorical. If True, the encoder will select all variables
-        or accept all variables entered by the user, including those cast as numeric.
+        If `ignore_format` is `False`, the encoder will automatically select variables
+        of type object or categorical, or check that the variables entered by the user
+        are of type object or categorical. If `True`, the encoder will select all
+        variables or accept all variables entered by the user, including those cast as
+        numeric.\n
+        In short, set to `True` when you want to encode numerical variables.
     """.rstrip()
+
 _unseen_docstring = """unseen: string, default='ignore'
         Indicates what to do when categories not present in the train set are
-        encountered during transform. If 'raise', then unseen categories will raise an
-        error. If 'ignore', then unseen categories will be set as NaN and a warning will
-        be raised instead.
+        encountered during transform. If `'raise'`, then unseen categories will raise
+        an error. If `'ignore'`, then unseen categories will be encoded as NaN and a
+        warning will be raised instead.
     """.rstrip()