Mark Goutte, Selenium, Sahi and Zombie driver/support as abandoned (#39)

* Mark Goutte, Selenium, Sahi and Zombie driver/support as abandoned

This marks the four drivers as abandoned where the driver implementations are no longer maintained.

* Correctly indent notes so they don't break the enumeration list

* Indent a few more notes that are part of a numerated list

UPGRADING.md

@@ -9,3 +9,18 @@ This document summarizes the changes relevant for users when upgrading to new ve
 The classes `FailureShowListener`, `SessionsListener` and `MinkExtension` have been marked as `@final`. They will become `final` classes in the next major release and you will no longer be able to use them by inheritance (https://github.com/FriendsOfBehat/MinkExtension/pull/41).
 
 Additionally, the two listener classes have been marked as `@internal`. Starting with the next major version, their API may change at any time without further notice.
+
+## Deprecated drivers
+
+Support for the following drivers has been deprecated, since the underlying driver implementations have been abandoned:
+
+- GoutteDriver
+- SeleniumDriver
+- SahiDriver
+- ZombieDriver
+
+The corresponding `Factory` classes will trigger a deprecation notice when they are used to build the driver, for example
+by using `goutte` as the driver identifier in the `behat.yml` configuration file (https://github.com/FriendsOfBehat/MinkExtension/pull/39/).
+
+Note, however, that Behat currently does not have a built-in mechanism to collect such deprecation notices and display
+them in a user-friendly way.