added INSTALL file

INSTALL

+CMAKE install procedure
+=======================
+
+The basic procedure to build and install macaon from sources is the following.
+- Create a build directory.
+  If the sources are in the macaon-X.X.X/ directory:
+    cd macaon-X.X.X
+    mkdir build
+    cd build
+- Launch the cmake command:
+    cmake ..
+
+  If you want to install macaon locally, you can specify the install path with :
+    cmake -DCMAKE_INSTALL_PREFIX:PATH=/absolute/path/to/macaon_install_dir
+
+- Build the sources with:
+    make
+- Install macaon
+    make install