Add sample CMake invocation to README.md

bootstrap/cxx/README.md

@@ -4,10 +4,23 @@ This directory contains a partial implementation of the Bolt programming
 language using C++ and LLVM. It currently is one of the main contenders of
 becoming the offical Bolt compiler.
 
-
 ## Developing
 
 You need a recent version of the Zen libries to be able to compile. If youu
 still get build errors, the Zen libraries might be out of date. Do not hesitate
 to file an issue!
 
+This is how a potential invocation to CMake could look like:
+
+```sh
+cmake \
+    -DCMAKE_CXX_COMPILER=clang++ \
+    -DCMAKE_BUILD_TYPE=Debug \
+    -DCMAKE_EXPORT_COMPILE_COMMANDS=ON \
+    -G Ninja \
+    -B build \
+    -DBOLT_ENABLE_TESTS=1 \
+    -DZEN_ENABLE_TESTS=0 \
+    -DLLVM_TARGETS_TO_BUILD=host \
+    -DLLVM_OPTIMIZED_TABLEGEN=ON
+```