added realm to htpasswd configuration, added bcrypt hint

The realm is required to prevent an InvalidConfigException in BasicAccessFactory from zendframework/zend-expressive-authentication-basic.

Since it's checked and RFC 2617 says "The realm attribute (case-insensitive) is required for all authentication schemes which issue a challenge.", it should be save to add it to the docs.

Also the .htpasswd file must use bcrypt hash algorithm, otherwise a RuntimeException is thrown.

Author: steffenbrand

docs/book/v1/user-repository.md

@@ -52,11 +52,12 @@ for more information on config providers.
 ## htpasswd configuration
 
 When using the htpasswd user repository implementation, you need only configure
-the path to the `htpasswd` file:
+the path to the `htpasswd` file and a `realm`. The `htpasswd` file must use bcrypt hash algorithm:
 
 ```php
 return [
     'authentication' => [
+        'realm' => 'insert realm value',
         'htpasswd' => 'insert the path to htpasswd file',
     ],
 ];