[glib: 1/2] docs: Clarify the meaning of --buildtype=plain a little

[Emmanuele Bassi <ebassi src gnome org>]

commit c33de0dc5fbcb9fb665944955f43d0f3b2c2f7d4
Author: Philip Withnall <pwithnall endlessos org>
Date:   Wed Nov 18 13:29:11 2020 +0000

    docs: Clarify the meaning of --buildtype=plain a little
    
    Signed-off-by: Philip Withnall <pwithnall endlessos org>
    
    Fixes: #1833

 docs/reference/glib/building.xml | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/docs/reference/glib/building.xml b/docs/reference/glib/building.xml
index 720a6ff84..9ff2fbfe7 100644
--- a/docs/reference/glib/building.xml
+++ b/docs/reference/glib/building.xml
@@ -216,6 +216,12 @@
         <literal>G_ENABLE_DEBUG</literal> will be defined and GLib will be built
         with additional debug code enabled.
       </para>
+      <para>
+        If the build type is <literal>plain</literal>, GLib will not enable any
+        optimization or debug options by default, and will leave it entirely to
+        the user to choose their options. To build with the options recommended
+        by GLib developers, choose <literal>release</literal>.
+      </para>
     </formalpara>
 
     <formalpara>