Added CMake options to the readme.

README.md

@@ -2,15 +2,15 @@
 and writes files in `${XDG_CONFIG_HOME}`. It creates subdirectories if
 necessary.
 
-### Dependencies
+## Dependencies
 
 * C++ compiler (Tested: g++ 5/8)
-* [cmake](https://cmake.org/)
+* [cmake](https://cmake.org/) (at least: 3.1)
 * [pkgconfig](https://pkgconfig.freedesktop.org/wiki/)
 * [libconfig++](https://github.com/hyperrealm/libconfig)
 * [libxdg-basedir](http://repo.or.cz/w/libxdg-basedir.git)
 
-### Usage
+## Install
 
 Copy `xdgcfg.hpp` into a folder where your project can find it.
 
@@ -22,8 +22,13 @@ make
 make install
 ```
 
+### CMake options
 
-### Documentation
+* `-DWITH_TESTS=YES` to compile the tests.
+* `-DWITH_EXAMPLES=YES` to compile the example.
+
+
+## Documentation
 
 `xdgcfg.hpp` has explanatory comments in it and there is an
 [example](src/example.cpp). The reference is also available at