Add Show Pending Migrations to rails til.

README.md

@@ -15,6 +15,7 @@ I shamelessly stole this idea from
 ## rails
 
 - [Attribute Was](rails/attribute-was.md)
+- [Show Pending Migrations](rails/show-pending-migrations.md)
 
 ## ruby
 

rails/show-pending-migrations.md

@@ -0,0 +1,23 @@
+# Show Pending Migrations
+
+Rails comes with a built-in rake task that allows you to check the status
+of migrations in the project.
+
+```bash
+$ rake db:migrate:status
+
+database: pokemon_development
+
+ Status   Migration ID    Migration Name
+--------------------------------------------------
+   up     20150219143706  Create pokemon table
+  down    20150228003340  Create stats table
+```
+
+For large projects with lots of migrations, this is going to be a lot of
+output, so you can trim it down with a simple `grep`:
+
+```bash
+$ rake db:migrate:status | grep '^  down'
+  down    20150228003340  Create stats table
+```