Better short description of task

Author: magec

README.md

@@ -29,7 +29,7 @@ utf8mb4 without truncating column contents and maintaining its original schema (
 
 ```
 ...
-rake db:utf8mb4                          # migrates a table (ENV["TABLE"]) to utf8mb encoding
+rake db:utf8mb4                          # migrates a table[/column] (TABLE, COLUMN env vars) to utf8mb encoding
 ...
 
 ```

lib/utf8mb4rails.rb

@@ -20,7 +20,7 @@ module Utf8mb4rails
   extend Rake::DSL
 
   namespace :db do
-    desc 'migrates a table (ENV["TABLE"]) to utf8mb encoding'
+    desc 'migrates a table[/column] (TABLE, COLUMN env vars) to utf8mb encoding'
     task utf8mb4: :environment do
       table = ENV['TABLE']
       unless table