feat: book decryption

All credits go to gawgua for his work, tysm.

README.md

@@ -13,7 +13,32 @@ pip install git+https://git.tretrauit.me/tretrauit/akademiya
 + [x] Authentication
 + [x] Look up books
 + [x] Borrow books
-+ [x] Download (encrypted) books
++ [x] Download & decrypt books
+
+## Building
+
+1. (Optional) You'll need to build the C++ part first, which can be built using CMake:
+> [!WARNING]
+> If you don't build the decryptor then the download function will not work.
+```bash
+cd decypherer
+mkdir build
+cd build
+# Linux & other platforms (Cross-compile)
+cmake -D CMAKE_BUILD_TYPE=Release ..  
+ninja
+# Windows (You need to have MSVC installed)
+cmake -G "Visual Studio 17" -DCMAKE_GENERATOR_PLATFORM=WIN32 .. 
+cmake --build . --config Release
+```
+
+2. Copy `decypherer.exe` to `bin/` directory.
+3. Run `python -m akademiya` to use as normal. 
+
+
+## Acknowledgements
+
++ [gawgua](https://github.com/gawgua): Reverse engineered the encryption system and wrote the decryption code.
 
 ## License