add optional readings for unsafe rust day

index.html

@@ -48,6 +48,9 @@
   - *Reading*:
     - [Rustnomicon chapter 1: Safe & Unsafe](https://doc.rust-lang.org/nomicon/meet-safe-and-unsafe.html) 
     - [How do programmers use unsafe rust?](./papers/unsafe_rust.pdf) by Vytautas Astrauskas et al.
+  - *Optional reading*:
+    - [Two Kinds of Invariants: Safety and Validity](https://www.ralfj.de/blog/2018/08/22/two-kinds-of-invariants.html)
+    - [Unsafe Rust and Miri](https://www.youtube.com/watch?v=svR0p6fSUYY&t=213s)
 
 Wed Oct 9 2024: Isolating untrusted code with Rust
   - *Reading*: