Add Slide-seq name to pdf titles

Small easy thing, I could probably even muster a PR.

When looking at pdf's across many different runs, it'd be nice to have the puckname on the page to make it easier to keep track of which is which. Shouldn't have to take up much screen real-estate either

E.g. 
```
UMIs per matched bead (Puck_210903_04)
```

Or 
```
UMIs per matched bead
Puck_210903_04 (subtitle)
```
