docs: the Wayland frontend composes too

It feeds the Compose table from the grab's keysyms like the other two; the
sentence was written when there were only two.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

README.md

@@ -58,9 +58,9 @@ a syllable — 한자 gives 漢字, 대한민국 gives 大韓民國 — and `Esc
 syllable back. Text already committed belongs to the application and
 cannot be converted.
 
-Dead keys and Compose sequences are composed by strans itself for the XIM
-and IBus frontends, from `XCOMPOSEFILE` or the locale; the GTK 3 module
-leaves them to GtkIMContextSimple.
+Dead keys and Compose sequences are composed by strans itself for the
+Wayland, XIM and IBus frontends, from `XCOMPOSEFILE` or the locale; the
+GTK 3 module leaves them to GtkIMContextSimple.
 
 ## Preedit and candidates