Update minimum boost version in Requirements

Change the boost version number to the oldest one we test in CI. Newer version might be required for recent compilers because of boost's compiler dependent macros.

README.md

@@ -36,7 +36,7 @@ CUDAHOSTCXX=`which g++` # full path to the C++ compiler to be used as CUDA host
 
 ##### Requirements
 - C++17 compiler (see also list of tested compilers)
-- Boost headers (1.65.1 or later)
+- Boost headers (1.77 or later)
 - CMake (3.18.1 or later)
 - CUDA Toolkit (11.0 or later, optional)
 - MPI (optional, CUDA-aware MPI for the GPU communication module `gcl_gpu`)