Simplify "basic installation" notes

Use the Rails-provided rake task for creating the dev database.

Change database-schema loading instructions, which is more future-proof.  Running migrations on the latest build resulted in this schema.rb difference:

    $ git status
    On branch master
    Your branch is up-to-date with 'origin/master'.
    Changes not staged for commit:
      (use "git add <file>..." to update what will be committed)
      (use "git checkout -- <file>..." to discard changes in working directory)

      modified:   ../db/schema.rb

    no changes added to commit (use "git add" and/or "git commit -a")
    $ cd ..
    $ git diff
    diff --git a/db/schema.rb b/db/schema.rb
    index 6c263e3..904a869 100644
    --- a/db/schema.rb
    +++ b/db/schema.rb
    @@ -95,7 +95,6 @@ ActiveRecord::Schema.define(:version => 20131101180159) do
         t.datetime "created_at",                                :null => false
         t.datetime "updated_at",                                :null => false
         t.string   "handle"
    -    t.boolean  "anonymous",              :default => false
         t.boolean  "guest",                  :default => false
         t.datetime "processing_timestamp"
         t.string   "access_token"

Author: eric-hu

README.md

@@ -32,8 +32,8 @@ On Mac OSX, you can use homebrew as package manager: http://mxcl.github.com/home
  * Copy and adjust database configuration (`cp config/database.yml.example config/database.yml`)
  * Copy secrets configuration (`cp config/secrets.yml.example config/secrets.yml`)
  * Copy s3 configuration (`cp config/s3.yml.example config/s3.yml`)
- * Create the database ggtracker needs (`mysql -u root` and then `create database ggtracker_development;` and then `quit`)
- * Run migrations (`bundle exec rake db:migrate`)
+ * Create the database ggtracker needs (`rake db:create`)
+ * Load the latest database schema (`bundle exec rake db:schema:load`)
 
 If you want to be able to upload replays, you'll need to have an
 Amazon S3 account.  After setting that up, edit your config/s3.yml