docs: Backspace gives the reach back

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

README.md

@@ -60,12 +60,15 @@ a syllable — 한자 gives 漢字, 대한민국 gives 大韓民國 — and `Esc
 syllable back. A word is committed a syllable at a time, so the reading
 also reaches back into the text the application already holds, as far as
 the dictionary knows the whole of it: type 한자 and then `Ctrl+H` and the
-query is 한자, not 자, and picking 漢字 takes the 한 back. A reading is
-also the start of the longer words it begins, whose conversions follow
-its own, so 대한 answers 大寒 first and 大韓民國 further down. A lone
-consonant is a reading too, and answers with the symbol table a Korean
-keyboard's 한자 key has always offered: ㅁ gives ※ ○ △ ㈜, ㄴ the brackets
-「」『』, ㄹ the units ℃ ㎏ ℓ, ㅇ the circled numbers ①②③.
+query is 한자, not 자, and picking 漢字 takes the 한 back. `Backspace`
+gives that reach back before it deletes what was typed, so 상 written
+with 태 typed answers 狀態, and one `Backspace` answers 態 for the
+syllable alone. A reading is also the start of the longer words it
+begins, whose conversions follow its own, so 대한 answers 大寒 first and
+大韓民國 further down. A lone consonant is a reading too, and answers
+with the symbol table a Korean keyboard's 한자 key has always offered:
+ㅁ gives ※ ○ △ ㈜, ㄴ the brackets 「」『』, ㄹ the units ℃ ㎏ ℓ, ㅇ the
+circled numbers ①②③.
 
 Reaching back needs the application to hand over the text around its
 cursor and to take some of it away again. The Wayland input method, IBus