Document how to choose compiler and set flags

Closes #5 (closed)

README.md

@@ -127,3 +127,21 @@ Intel C++ Compiler should be used with `NMake Makefiles`, MinGW C++ should be us
 ```
 cmake -B . -S ../exple-cmake-build -G"Visual Studio 17 2022"
 ```
+
+### Choosing a compiler and setting compiler options
+
+To choose a compiler use *CMAKE_CXX_COMPILER* variable when configuring cmake build. For setting options to be passed to compiler during build use *CMAKE_CXX_FLAGS* variable.
+
+If you have *icc* on path, i.e.
+```
+icc --version
+```
+returns the version number then you can select it as a compiler for building this project with
+```
+cmake -B . -S ../exple-cmake-build -DCMAKE_CXX_COMPILER=icc
+```
+To specify compilation options, e.g. *-fno-align-loops* and *-fno-align-loops*
+```
+cmake -B . -S ../exple-cmake-build -DCMAKE_CXX_COMPILER=icc -DCMAKE_CXX_FLAGS="-fno-align-loops -fno-align-loops"
+```
+