Set expectations better around paper reading

1. We should call out in the sprint workbook / distributed systems primer that there's a "read some papers and book time to discuss them" element which may take disproportionate time, and needs planning
2. We should call out how many papers we expect the fellows to read - sprint 2 currently has 5 pretty beefy papers, and this is also probably our fellows' first experience of reading academic papers, so we should expectation set how many of them we expect them to read (and how much depth to go into)