Add an example of using Crypto3 with clang (non-zkllvm) compiler

[NickVolynkin]

Developers need an example of how to use Crypto3 in the standard development workflow. That is, compile code into an executable and run unit tests. This example would be enough:

auto a = hashes::sha2<256>::block_type {1}
auto b = hashes::sha2<256>::block_type {2}
bool matched = hash<hashes::sha2<256>>(a, b) == ff55c97976a840b4ced964ed49e3794594ba3f675238b5fd25d282b60f70a194;
std::cout << matched;

See also NilFoundation/zkllvm-template#27

[nkaskov]

Hashes return byteblob. Thus you cannot compare it with ff55c97976a840b4ced964ed49e3794594ba3f675238b5fd25d282b60f70a194
Besides, C++ does not support such long constants.

Possible solution: make byte array from this number and compare with the output of hash function.