Restructure ability documentation

app.py

@@ -229,7 +229,7 @@ class PersonLayout(ParameterLayout):
 
     def extra(self, df, *args):
         with gr.Row():
-            with gr.Column('Compare ability'):
+            with gr.Column():
                 gr.Markdown(self.text)
 
             with gr.Column(scale=3):

docs/ability.md

@@ -1,10 +1,11 @@
-## Probability that Model 1 is preferred to Model 2
+### Ability comparison
 
 Select two models to compare their abilities. The generated histogram
 represents the distribution of the difference in estimated model
-abilities:
+abilities: the probability that Model 1 is stronger than to Model
+2. In the figure:
 
-* The dashed vertical line is its median.
+* The dashed vertical line is the median.
 * The shaded region demarcates the chosen [highest density
   interval](https://cran.r-project.org/package=HDInterval) (HDI).
 * The note in the upper left denotes the smallest HDI that is