Update INSTALL by adding cross-compile guide for OpenHarmony

Signed-off-by: kuniqi <[email protected]>

Author: kuniqi

INSTALL

@@ -133,6 +133,10 @@ this:
                  CXX="g++ -arch i386 -arch x86_64 -arch ppc -arch ppc64" \
                  CPP="gcc -E" CXXCPP="g++ -E"
 
+  For OpenHarmony cross-compile system, you can follow this document 
+(https://gitcode.com/openharmony-sig/tpc_c_cplusplus/blob/master/Cross-Com
+pilation Guide for Open-Source Third-Party Libraries in OpenHarmony_en.md)
+
    This is not guaranteed to produce working output in all cases, you
 may have to build one architecture at a time and combine the results
 using the 'lipo' tool if you have problems.