[retro-gtk] README.md: update compiling instruction

[Adrien Plazas <aplazas src gnome org>]

commit a05cf49131b88b4ee25244a30c161fe1785b52c9
Author: RoubyPA <pa rouby gmail com>
Date:   Mon Nov 27 10:57:01 2017 +0100

    README.md: update compiling instruction
    
    https://bugzilla.gnome.org/show_bug.cgi?id=790454

 README.md | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)
---
diff --git a/README.md b/README.md
index 0c17d07..7c5b1f9 100644
--- a/README.md
+++ b/README.md
@@ -17,15 +17,14 @@ retro-gtk depends on the following libraries at compile time and at run time:
 ## Compiling
 
 To configure the compilation, do:
-`./autogen.sh`
+`meson build`
 
 You can specify the installation prefix by doing:
-`./autogen.sh --prefix /my/prefix`
+`meson build --prefix /my/prefix`
 
 Then compile:
-`./configure`
-`make`
+`ninja -C build`
 
 ## Installing
 
-`make install`
+`ninja -C build install`