add example of dataframe access and minor spelling fixes (#20)

Co-authored-by: Johnny Bui <[email protected]>

Author: TypingKoala

docs/intro/firststeps.rst

@@ -230,7 +230,7 @@ Styling
 =======
 
 Now that the Evaluation has been processed, we can add styling so that
-important information stands out in the final visualization. This is achived
+important information stands out in the final visualization. This is achieved
 through a special type of Processor called :ref:`topics-styles`. 
 
 Styles are also run in a processing pipeline, but they always output CSS strings.

docs/topics/evaluation.rst

@@ -21,6 +21,30 @@ transform the evaluation one-at-a-time.
 Extracting the internal dataframe
 =================================
 Evaluations store the test results internally using a Pandas dataframe. You can
-retrive this dataframe by using the ``get_df()`` method.
+retrieve this dataframe by using the ``get_df()`` method. This can be used to
+manipulate the underlying data without needing to use the built-in FTPVL processors.
 
-.. automethod:: ftpvl.evaluation.Evaluation.get_df
+.. note:: ``get_df()`` returns a defensive copy of the dataframe, so any 
+    mutations to the returned dataframe will not be reflected in the original
+    Evaluation. Instead, you must instantiate a new ``Evaluation`` by passing
+    in the dataframe and evaluation ID.
+
+.. automethod:: ftpvl.evaluation.Evaluation.get_df
+
+Example
+*******
+
+.. code-block:: python
+
+    >>> eval1 = Evaluation(pd.DataFrame([{"a": 1, "b": 2}, {"a": 4, "b": 5}]), eval_id=1)
+    >>> df = eval1.get_df() # extract Pandas dataframe
+    >>> df
+        a   b
+    0   1   2
+    1   4   5
+    >>> df["c"] = [3, 6] # add a new column
+    >>> eval2 = Evaluation(df, eval_id=eval1.get_eval_id()) # create new evaluation
+    >>> eval2.get_df()
+        a   b   c
+    0   1   2   3
+    1   4   5   6

docs/topics/visualizers.rst

@@ -16,7 +16,7 @@ You can choose to show the version info of each test result by setting the
 the display of the version info that is provided by Hydra.
 
 
-Displaying the Visualizaton
+Displaying the Visualization
 ============================
 After instantiating the desired visualizer, you can call the 
 ``get_visualization()`` method to return an object that can be displayed in an