Update schedule: add GPU and serial code links for lectures 16-17

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: alanedelman

README.md

@@ -65,7 +65,7 @@ Take a look at [MIT Engaging](https://engaging-ood.mit.edu:8443/auth/realms/enga
 | | 3/25/2026 | Wednesday | Spring Break | | |
 | 15 | 3/30/2026 | Monday | | Alan | Parallel Prefix [[prefix spring 2026.pptx]](https://github.com/mitmath/18337/blob/master/prefix%20%20spring%202026.pptx) [[prefixspring2026.jl]](https://github.com/mitmath/18337/blob/master/prefixspring2026.jl) |
 | 16 | 4/1/2026 | Wednesday | | Alan | Into to GPUS [[gpus2026.pptx]](https://github.com/mitmath/18337/blob/master/gpus2026.pptx) |
-| 17 | 4/6/2026 | Monday | | Alan | |
+| 17 | 4/6/2026 | Monday | | Alan | [Optimizing Serial Code](https://book.sciml.ai/notes/02-Optimizing_Serial_Code/) |
 | 18 | 4/8/2026 | Wednesday | | Alan | |
 | 19 | 4/13/2026 | Monday | | Alan | |
 | 20 | 4/15/2026 | Wednesday | | Alan | |