fix: update readme

README.md

@@ -7,6 +7,7 @@ Required dependencies:
   - `riscv64-unknown-elf-gcc`
 - `gcc`
 - Python 3
+- 7z (7-zip CLI)
 
 
 ```sh
@@ -20,6 +21,19 @@ 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]`
+## Configuration
+Some challenge parameters can be set with environment variables.
+The provided `.env.example` file contains a sample configuration.
 
+- `FLAG_LEN`: Number, the length of the flag
+- `FLAG_FORMAT`: String, containing the constant `FLAG_GOES_HERE` to be replaced by the flag
+- `ENCRYPTOR_VENDOR_ID`: String, overwrite CPU vendor id. Will use system information if unset
+- `ENCRYPTOR_MODEL_NAME`: String, overwrite CPU model name. Will use system information if unset
+- `ENCRYPTOR_OS_VERSION`: String, overwrite OS version. Will use system information if unset
+- `ENCRYPTOR_MEM_TOTAL`: String, overwrite total memory (in kB). Will use system information if unset
+
+
+
+## Running the challenge
+- The built binary is at `build/main[.exe]`
+- The binary together with the encrypted license file is packaged in `build/challenge.zip`