docs: add readme

README.md

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+# SAS Project 2026 - Program
+
+## Building
+
+Required dependencies:
+- `riscv64-unknown-elf` toolchain
+  - `riscv64-unknown-elf-gcc`
+- `gcc`
+- Python 3
+
+
+```sh
+make
+```
+
+### Getting the flag
+
+Compiling with `make` will print the correct flag to stderr, e.g.:
+```
+[Codegen] Generated Flag: ctf{3P1WBAldo2PxYZtJIoadV_NnL1nueJAbVDtMiJhY0vQ}
+```
+
+## Running the challenge
+The built binary is at `build/main[.exe]`
+