[gtksourceview] build: update build instructions

[Christian Hergert <chergert src gnome org>]

commit 0cf0a283c4bfa491fe8c65c64ac2adec73d821fa
Author: Jordi Mas <jmas softcatala org>
Date:   Mon Apr 29 20:11:58 2019 +0200

    build: update build instructions

 README | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)
---
diff --git a/README b/README
index 20112324..e801f0bc 100644
--- a/README
+++ b/README
@@ -28,17 +28,14 @@ Installation
 
 Simple install procedure from a tarball:
 
-  $ ./configure
-  $ make
+  $ mkdir build
+  $ meson build
+  $ cd build
   [ Become root if necessary ]
-  $ make install
+  $ ninja install
 
 See the file 'INSTALL' for more detailed information.
 
-From the Git repository, the 'configure' script and the 'INSTALL' file are not
-yet generated, so you need to run 'autogen.sh' instead, which takes the same
-arguments as 'configure'.
-
 To build the latest version of GtkSourceView plus its dependencies from Git,
 Jhbuild is recommended: