Fix slightly-less-easy install instructions

Running the install instructions as documented, I get an error in bash:

```console
maciek@gamera:~/code/mongolike$ psql mongolike-test <sql/*.sql
bash: sql/*.sql: ambiguous redirect
```

I don't think it's possible to redirect input from multiple files like this. Looping over the files works for me.
Merge pull request #13 from deafbybeheading/patch-1

Fix slightly-less-easy install instructions