Update README.md

Author: sawenzel

README.md

@@ -9,3 +9,9 @@ It offers:
 
   * llvm + clang + clang extra tools (release 3_9) required
   * build using `cmake -DLLVM_DIR=PATH_TO_LLVM_CMAKE_CONFIG -DClang_DIR=PATH_TO_CLANG_CONFIG`
+
+# Usage
+
+In the build directory of AliceO2 (containing the CMake compilations database in form of `compile_command.json`), run
+
+`run_O2CodeChecker.py -checks=-*,alice* `