[cantarell-fonts] Update README.md with glyphsLib 2.3.0 information

[Nikolaus Waxweiler <nwaxweiler src gnome org>]

commit 213f1e876f47a62ac415e05a88af9b969f3dbfb8
Author: Nikolaus Waxweiler <madigens gmail com>
Date:   Mon Mar 26 20:44:00 2018 +0000

    Update README.md with glyphsLib 2.3.0 information

 README.md | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index 71840535..b15851e2 100644
--- a/README.md
+++ b/README.md
@@ -32,10 +32,11 @@ Given the decaying state of FontForge (arcane user interface, heaps of quirky an
 Developer information
 ---------------------
 
-The master file is `src/Cantarell.glyphs`. To contribute, you need to either:
+The master file is `src/Cantarell.glyphs`. To contribute, you need to:
 
 -      Use the proprietary and Mac-only Glyphs.app...
 -      ...or generate UFOs from it by using `fontmake -g src/Cantarell.glyphs -o ufo`. You can then open the 
masters in `master_ufo` with any design app that supports it. Send the contribution to Nikolaus Waxweiler 
somehow so he can consider it.
+-      ...or wait for glyphsLib 2.3.0 to be released, which will finally contain code to roundtrip between 
Glyphs files and UFOs, at which point I'll switch over and you'll be able to use any UFO editor you'd like. 
Rejoice!
 
 Acknowledgements
 ----------------