[gobject-introspection/wip/hadess/document-glib-gir] HACKING: Document how to update glib GIR

[Bastien Nocera <hadess src gnome org>]

commit 65c4b00f9bae38a095c68870137a39ea27006944
Author: Bastien Nocera <hadess hadess net>
Date:   Thu Feb 20 12:35:18 2020 +0100

    HACKING: Document how to update glib GIR
    
    Closes: https://gitlab.gnome.org/GNOME/gobject-introspection/issues/320

 HACKING | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)
---
diff --git a/HACKING b/HACKING
index b5c9c81c..282f3c25 100644
--- a/HACKING
+++ b/HACKING
@@ -1,6 +1,22 @@
 Notes to developers hacking on GObjectIntrospection
 ===================================================
 
+updating GLib bindings
+----------------------
+
+Some bindings are not generated by the libraries themselves, usually
+for dependency reasons, but are updated through some ad hoc utilities.
+
+Updating GLib, Gio, GModule, GObject bindings:
+```sh
+$ git clone https://gitlab.gnome.org/GNOME/glib.git
+$ meson _build
+$ ninja -C _build
+$ ./misc/update-glib-annotations.py glib/
+```
+
+In short, build gobject-introspection in the `_build` directory, and
+run the script on a `glib` checkout.
 
 debugging
 ---------