docs: Add a README.rationale documenting major design decisions

It will be useful to document the major decisions which affect the whole
of GLib in one centralised, easily-greppable file, otherwise they will
get lost forever in Bugzilla.

This file should contain a brief explanation of the decision and its
rationale, plus a link to further discussion (e.g. on a mailing list or
bug report).

This contains an initial discussion about use of compiler attributes in
GLib.

https://bugzilla.gnome.org/show_bug.cgi?id=113075

HACKING

@@ -33,4 +33,5 @@ Note that autogen.sh runs configure for you.  If you wish to pass
 options like --prefix=/usr to configure you can give those options
 to autogen.sh and they will be passed on to configure.
 
-For information about submitting patches see the README.commits file.
+For information about submitting patches see the README.commits file. For
+information about major design decisions, see the README.rationale file.

Makefile.am

@@ -40,6 +40,7 @@ EXTRA_DIST += 			\
 	sanity_check		\
 	README.commits		\
 	README.in		\
+	README.rationale	\
 	INSTALL.in		\
 	README.win32		\
 	HACKING			\

README.rationale

@@ -0,0 +1,10 @@
+This file documents various major decisions which affect GLib development,
+giving a brief rationale of each decision, plus a link to further discussion.
+
+
+ * Compiler attributes: https://bugzilla.gnome.org/show_bug.cgi?id=113075#c46
+
+   GLib uses GIR annotations instead of compiler attributes. They are tidier,
+   already supported by GLib and GNOME tools, and accomplish the same task as
+   compiler attributes. GLib does not provide macros for attributes like
+   nonnull because it would not use them.