Describe the intent of the WD context role

[skip ci]

lib/Selenium/Remote/Driver/CanSetWebdriverContext.pm

@@ -3,6 +3,21 @@ package Selenium::Remote::Driver::CanSetWebdriverContext;
 # ABSTRACT: Customize the webdriver context prefix for various drivers
 use Moo::Role;
 
+=head1 DESCRIPTION
+
+Some drivers don't use the typical C</wd/hub> context prefix for the
+webdriver HTTP communication. For example, the newer versions of the
+Firefox driver extension use the context C</hub> instead. This role
+just has the one attribute with a default webdriver context prefix,
+and is consumed in L<Selenium::Remote::Driver> and
+L<Selenium::Remote::RemoteConnection>.
+
+If you're new to webdriver, you probably want to head over to
+L<Selenium::Remote::Driver>'s docs; this package is more of an
+internal-facing concern.
+
+=cut
+
 has 'wd_context_prefix' => (
     is => 'lazy',
     default => sub { '/wd/hub' }