Merge pull request #9 from ogom/brew_switch

Add brew switch to README

Patch by @ogom, thanks!

README.md

@@ -10,6 +10,12 @@ With MariaDB:
     % brew tap mroonga/mroonga
     % brew install mroonga --use-homebrew-mariadb
 
+If you have an old formulae, please unlink to the old formulae version:
+
+    % brew services stop [formulae]
+    % brew unlink [formulae]
+    % mv /usr/local/var/[formulae] /usr/local/var/[formulae_version]
+
 If you want to use this formula with MySQL built by yourself instead of MySQL installed by Homebrew:
 
     % curl -O http://ftp.jaist.ac.jp/pub/mysql/Downloads/MySQL-5.5/mysql-5.5.24.tar.gz