[gdk-pixbuf] docs: Update the option used to generate the API reference

[Emmanuele Bassi <ebassi src gnome org>]

commit 79798c0aafe5f2e3cb1546696e2a353f403a200d
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Fri Jun 26 11:47:53 2020 +0100

    docs: Update the option used to generate the API reference
    
    We use `gtk_doc`, now.

 README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index e95e9fc60..f6fd10e18 100644
--- a/README.md
+++ b/README.md
@@ -71,7 +71,7 @@ You can specify the following options in the command line to `meson`:
  * `-Djasper=true` - Enable support for JPEG2000.  This requires
    [libjasper's development files](http://www.ece.uvic.ca/~frodo/jasper/)
    to be installed.
- * `-Ddocs=true` - Build the API reference documentation.  This
+ * `-Dgtk_doc=true` - Build the API reference documentation.  This
    requires `gtk-doc` to be installed.
  * `-Drelocatable=true` - Enable application bundle relocation support.