Boost.compute no longer a self contained library?

In the official Boost.Compute [documentation](https://www.boost.org/doc/libs/1_69_0/libs/compute/doc/html/boost_compute/getting_started.html#boost_compute.getting_started.compilation_and_usage), the tutorial starts with how to get Boost.Compute running as succinctly as:

`g++ -I/path/to/compute/include main.cpp -lOpenCL`

But it won't work.

It seems we also need to add Boost in the include path, as many source files need Boost library features such as `BOOST_STATIC_ASSERT()`. So maybe the tutorial can be updated to clear up some confusions

The tutorial also implies no external dependencies are needed. I need to define macro `BOOST_COMPUTE_NO_BOOST_CHRONO` to disable linking with `libboost_chrono`. Again it seems to go undocumented too

For reference, here is my cmake script for compiling `example/hello_world.cpp` to make it compile without external dependencies.

```cmake
find_path(BoostCompute_INCLUDE_DIRS
NAME boost/compute.hpp
PATHS /repo/boost.compute/include)
find_package(OpenCL REQUIRED)
find_package(Boost 1.54 REQUIRED)

add_executable(compute_hello_world hello_world.cpp)
target_include_directories(compute_hello_world PRIVATE
${BoostCompute_INCLUDE_DIRS}
${OpenCL_INCLUDE_DIRS}
${Boost_INCLUDE_DIRS}
)
target_link_libraries(compute_hello_world
${OpenCL_LIBRARIES}
)
target_compile_definitions(compute_hello_world PRIVATE
BOOST_COMPUTE_NO_BOOST_CHRONO # disable linking with boost chrono library
)
```