Maybe document quickloading 'staticl/format/spinneret'

When evaluating
```lisp
(staticl:generate :root-dir "/tmp/my-site"
:stage-dir "/tmp/result")
```

I get an error:
```
; Evaluation aborted on Component "spinneret" not found, required by
; #.
```

`staticl/format/spinneret` isn't listed as a dependency in the asd file, so the systems/deps it needs don't get pulled in by default when installing staticl (which might be a good thing). In https://40ants.com/staticl/making-a-site/#initializing-static-for-the-site it might be a good idea to mention needing to quickload it to grab dependencies:

```lisp
(ql:quickload :staticl/format/spinneret)
```