some cleanup

readme.md

@@ -13,3 +13,4 @@ Differences between the Go and the Python, as well as notes more generally:
 * The Value struct has actual tests confirming the backward propagation logic.
 * When writing the Value struct and its methods, I accidentally swapped the order of the values in the `localGrads` slice in `Mul` and tore my hair out trying to figure out where the bug was. When I broke down and asked copilot to "compare these two implementations and tell me how they differ," it managed to find the error -- but also reported three non-existent differences and told me that `slices.Backward()` doesn't exist.
 * Initial pass translating the linear algebra functions has me worried that all those value structs aren't going to be very fast...
+* Had to implement weighted random choice. <https://cybernetist.com/2019/01/24/random-weighted-draws-in-go/> made that relatively straightforward; it's a neat algorithm.