cross compile guide

now the imgeditor depend on libcrypt.so, we should set a prefix path to make cmake find it.

➜  imgeditor git:(master) ✗ mkdir build-arm64 
➜  imgeditor git:(master) ✗ cd build-arm64 
➜  build-arm64 git:(master) ✗ cmake -DCMAKE_C_COMPILER=aarch64-linux-gnu-gcc -DCMAKE_PREFIX_PATH=/home/extlibs/install/ARM64 ..
-- The C compiler identification is GNU 11.3.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /opt/gcc-linaro-11.3.1-2022.06-x86_64_aarch64-linux-gnu/bin/aarch64-linux-gnu-gcc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Found OpenSSL: /home/extlibs/install/ARM64/lib/libcrypto.so (found version "1.1.1l")
-- Auto generated version: v1.0.0-17-gd6c63f1
-- Configuring done (0.3s)
-- Generating done (0.0s)
-- Build files have been written to: /home/imgeditor/build-arm64
➜  build-arm64 git:(master) ✗ make