cmake: add generator flag, help example (#10087)

* cmake: Add generator flag

* Add help example & generator list

pages/common/cmake.md

@@ -11,6 +11,10 @@
 
 `cmake {{path/to/project_directory}} -D {{CMAKE_BUILD_TYPE=Release}}`
 
+- Generate a build recipe using `generator_name` as the underlying build system:
+
+`cmake -G {{generator_name}} {{path/to/project_directory}}`
+
 - Use a generated recipe in a given directory to build artifacts:
 
 `cmake --build {{path/to/build_directory}}`
@@ -26,3 +30,7 @@
 - Run a custom build target:
 
 `cmake --build {{path/to/build_directory}} --target {{target_name}}`
+
+- Display help, obtain a list of generators:
+
+`cmake --help`