dev: add a colorize section to the scratch sample wiki

The sample wiki had no place to exercise :VimwikiColorize. Add a "Colour
spans" section to Syntax.wiki with words/phrases to wrap (and an already-
colorized span to render), plus a pointer in index.wiki's "Commands to
try" list. Lets the start-* launchers smoke-test the colorize fix.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

development/_common.sh

@@ -78,6 +78,7 @@ One page per feature group:
 - :NuwikiGenerateLinks
 - :NuwikiCheckLinks
 - :NuwikiMakeDiaryNote
+- :VimwikiColorize red — on a word in [[Syntax]] (or <Leader>wc)
 
 :sample:smoke-test:sandbox:
 EOF
@@ -92,6 +93,18 @@ Back to [[index]].
 *bold*, _italic_, *_bold italic_*, ~~strikethrough~~, `inline code`,
 super^script^ and sub,,script,,, and inline math $e^{i\pi} + 1 = 0$.
 
+== Colour spans (:VimwikiColorize) ==
+
+Put the cursor on a word and run `:VimwikiColorize red` (or press
+`<Leader>wc` and type a colour); or visually select a phrase and press
+`<Leader>wc`. Each wraps the target in `<span style="color:…">…</span>`.
+
+- colorize this important word
+- now select and colour this whole phrase
+- hex works too: paint deepskyblue on this token
+
+Already colorized: <span style="color:#1e90ff">dodger blue</span>.
+
 == Keywords ==
 
 TODO STARTED FIXME XXX DONE FIXED STOPPED