Add new test: captcha

Author: jserv

README.md

@@ -146,7 +146,8 @@ See [CONTRIBUTING.md](CONTRIBUTING.md) for contribution guidelines.
 ## External sources
 
 In `rv32emu` repository, there are some prebuilt ELF files for testing purpose.
-* `chacha20.elf` : See [tests/chacha20](tests/chacha20)
+* `captcha.elf` : See [tests/captcha.c](tests/captcha.c)
+* `chacha20.elf` : See [tests/chacha20](tests/chacha20.c)
 * `coremark.elf` : See [eembc/coremark](https://github.com/eembc/coremark) [RV32M]
 * `dhrystone.elf` : See [rv8-bench](https://github.com/michaeljclark/rv8-bench)
 * `doom.elf` : See [sysprog21/doom_riscv](https://github.com/sysprog21/doom_riscv) [RV32M]