Give example docstring one-line summary (#36158)

Point 2 of conventions immediately below this example calls for one line summary.

Closes #36147

Author: non-Jedi

doc/src/manual/documentation.md

@@ -29,8 +29,9 @@ Here is a more complex example, still using Markdown:
 """
     bar(x[, y])
 
-Compute the Bar index between `x` and `y`. If `y` is missing, compute
-the Bar index between all pairs of columns of `x`.
+Compute the Bar index between `x` and `y`.
+
+If `y` is unspecified, compute the Bar index between all pairs of columns of `x`.
 
 # Examples
 ```julia-repl