Add info regarding MySQL INDEX permissions

README.txt

@@ -28,9 +28,12 @@ system. Textpattern is both free and open source.
   instructions:
     http://textpattern.com/hidden-files-osx
 * Create or verify the existence of a working MySQL database with valid username
-  and password, then load /textpattern/setup/
-  (or /subdirectory/textpattern/setup/) in your browser to start the
-  installation process and follow the directions.
+  and password. From Textpattern 4.6.0, the MySQL database user requires INDEX
+  permissions in addition to standard SELECT, CREATE, UPDATE, ALTER, etc
+  permissions. See the system requirements for a complete list:
+    http://textpattern.com/about/119/system-requirements
+* Load /textpattern/setup/ (or /subdirectory/textpattern/setup/) in your
+  browser to start the installation process and follow the directions.
 * When the installation is complete, remove the /textpattern/setup/ directory
   from your site.
 
@@ -41,6 +44,8 @@ system. Textpattern is both free and open source.
     http://textpattern.com/about/119/system-requirements
 * Log out of the Textpattern admin-side.
 * Verify the existence of a known-good Textpattern database and file backup.
+* Ensure your MySQL database user has INDEX permissions in addition to any
+  permissions previously granted.
 * Replace the top-level index.php, css.php and .htaccess files, everything in
   the /js/ directory, everything in the /rpc/ directory and everything in the
   /textpattern/ directory (except /textpattern/config.php) with the