Merge branch 'feature/readme' into 'master'

add a meaningful readme file

See merge request spraetor/dune-gmsh4!6

README

-Preparing the Sources
-=========================
-
-Additional to the software mentioned in README you'll need the
-following programs installed on your system:
-
-  cmake >= 2.8.12
-
-Getting started
----------------
-
-If these preliminaries are met, you should run
-
-  dunecontrol all
-
-which will find all installed dune modules as well as all dune modules
-(not installed) which sources reside in a subdirectory of the current
-directory. Note that if dune is not installed properly you will either
-have to add the directory where the dunecontrol script resides (probably
-./dune-common/bin) to your path or specify the relative path of the script.
-
-Most probably you'll have to provide additional information to dunecontrol
-(e. g. compilers, configure options) and/or make options.
-
-The most convenient way is to use options files in this case. The files
-define four variables:
-
-CMAKE_FLAGS      flags passed to cmake (during configure)
-
-An example options file might look like this:
-
-#use this options to configure and make if no other options are given
-CMAKE_FLAGS=" \
--DCMAKE_CXX_COMPILER=g++-5 \
--DCMAKE_CXX_FLAGS='-Wall -pedantic' \
--DCMAKE_INSTALL_PREFIX=/install/path" #Force g++-5 and set compiler flags
-
-If you save this information into example.opts you can pass the opts file to
-dunecontrol via the --opts option, e. g.
-
-  dunecontrol --opts=example.opts all
-
-More info
----------
-
-See
-
-     dunecontrol --help
-
-for further options.
-
-
-The full build system is described in the dune-common/doc/buildsystem (Git version) or under share/doc/dune-common/buildsystem if you installed DUNE!

README.md

+# Dune-Gmsh4
+File reader for the Gmsh MSH file format version 4.
+
+## Summary
+Provides a file reader to read MSH file format version 4. It supports various
+grid-creator policies. Higher-order parametrized grids can be read using a
+`LagrangeGridCreator`.
+
+## Usage
+Either construct a grid directly
+```c++
+#include <dune/gmsh4/gmsh4reader.hh>
+#include <dune/gmsh4/gridcreators/lagrangegridcreator.hh>
+#include <dune/grid/uggrid.hh>
+
+int main()
+{
+  using namespace Dune;
+  using Grid = UGGrid<2>;
+  std::unique_ptr grid = Gmsh4Reader<Grid>::createGridFromFile("filename.msh");
+}
+```
+
+or explicitly use a grid-creator
+```c++
+#include <dune/foamgrid/foamgrid.hh>
+#include <dune/gmsh4/gmsh4reader.hh>
+#include <dune/gmsh4/gridcreators/lagrangegridcreator.hh>
+
+int main()
+{
+  using namespace Dune;
+  using Grid = FoamGrid<2,3>;
+  GridFactory<Grid> factory;
+  Gmsh4::LagrangeGridCreator creator{factory};
+  Gmsh4Reader reader{creator};
+
+  reader.read("filename.msh");
+  auto grid = factory.createGrid();
+}
+```
+Note, the grid-creator itself is a grid-function.
\ No newline at end of file