Some description in gemspec to make it valid

Otherwise:

```
Using suwabara (0.0.1) from git://github.com/whitequark/suwabara.git (at master)
suwabara did not have a valid gemspec.
This prevents bundler from installing bins or native extensions, but that may not affect its functionality.
The validation message from Rubygems was:
  "FIXME" or "TODO" is not a description
```