Fix documentation: stop __init__ rendering in bold

Summary:
Requires
https://secure.phabricator.com/rPHU0acf708b9b0fdbf59e4399f14dd8295b6a96972c
from libphutil, which allows a backslash prefix to control escape
sequences such as bold, underline, and invert.

Test Plan: "arc help liberate"
Reviewed By: epriestley
Reviewers: epriestley
CC: aran, epriestley
Differential Revision: 767

src/workflow/liberate/ArcanistLiberateWorkflow.php

@@ -34,7 +34,7 @@ class ArcanistLiberateWorkflow extends ArcanistBaseWorkflow {
       **liberate** [__path__]
           Supports: libphutil
           Create or update a libphutil library, generating required metadata
-          files like __init__.php.
+          files like \__init__.php.
 EOTEXT
       );
   }