message: README: recommend out of tree build
diff: @@ -67,7 +67,9 @@ but calls CMake with CMake-style parameters.
  Installation from source code is performed using the CMake toolchain.
  ```shell
  -cmake .
  +mkdir build
  +cd build
  +cmake ..
  make
  make install
  ```
  @@ -87,7 +89,9 @@ If you are building from git, you will need to run `./autogen.sh` first to
  produce the `configure` script.
  ```shell
  -./configure
  +mkdir build
  +cd build
  +../configure
  make
  make install
  ```
  