Add readme

README.md

-# cpp-tools
+# cpp_tools : small cpp tools to reuse in you projects
+
+`cpp_tools` is a collection of headers organised as modules.
+The fisrt effort here, is to use this repository as a submodule in your lib/app.
+
+For now, the following modules are available :
+ - cl_parser : a command line parser to pass command line arguments to your binaries.
+ - parallel_manager : a utility class to manage mpi and openmp.
+ - colors : a terminal coloring tool.
+ - timers : a collection of timers for benchmarking/tracing your lib/app.
+
+## Using this repo as a git submodule
+
+One you have added this repo as a submodule to your own repo, `cpp_tools` provides
+a simple way to initialyse the tools in your cmake.
+
+First you need to update your cmake module path with the path to root of the submodule :
+
+```cmake
+list(APPEND CMAKE_MODULE_PATH ${CMAKE_CURRENT_SOURCE_DIR}/path/to/cpp_tools/)
+```
+Then you need to set the `CPP_TOOLS_ROOT` variable with the path to the root of
+the submodule to make `cpp_tools` aware of its own location :
+
+```cmake
+set(CPP_TOOLS_ROOT ${CMAKE_CURRENT_SOURCE_DIR}/path/to/cpp_tools/)
+```
+Now you need to specify which modules you want to use :
+
+```cmake
+set(CPP_TOOLS_USE_CL_PARSER ON)
+set(CPP_TOOLS_USE_COLORS ON)
+set(CPP_TOOLS_USE_TIMERS ON)
+set(CPP_TOOLS_USE_PARALLEL_MANAGER ON)
+```
+And then include the `init-cpptools.cmake` file in your cmake to initialise `cpp_tools` : 
+
+```cmake
+include(cmake/init-cpptools)
+```
+
+This will give you access to the following targets :
+ - cpp_tools::cl_parser
+ - cpp_tools::colors
+ - cpp_tools::timers
+ - cpp_tools::parallel_manager
+
+Now, you just have to use these targets in your cmake !
+
+```cmake
+target_link_libraries(myexe PRIVATE cpp_tools::colors cpp_tools::cl_parser)
+```
+
+## Exporting and installing
+
+If `cpp_tools` becomes a dependency for you, and you need to forwad its 
+headers in your installation process, you can do it as follow.
+
+First you need to include `export-cpptools.cmake` in your cmake intall process.
+
+```cmake
+include(cmake/export-cpptools)
+```
+
+This will generate all the target you need as dependencies (i.e `cpp_tools::colors` etc)
+in the following folder `/your/install/prefix/lib/cmake/cpp_tools/` and copy the include files
+required in `/your/install/prefix/include/cpp_tools/`.
+
+Now you need to add the following entry in your `package-nameConfig.cmake.in` file *BEFORE* you include your project targets :
+```cmake
+...
+  include("@CMAKE_INSTALL_PREFIX@/lib/cmake/cpp_tools/cpp-tools-targets.cmake")
+  include("@CMAKE_INSTALL_PREFIX@/lib/cmake/@YOUR_PROJECT_NAME@/@YOUR_PROJECT_NAME@-targets.cmake")
+...
+```
+And that's it !
+