docs: update README to include note on always-enabled spoiler syntax

Author: hryhoriiK97

README.md

@@ -32,6 +32,8 @@
 - 🔄 Smart copy/paste with Markdown preservation
 - 🎨 Customizable bold, italic, and link colors
 
+> **Note:** Spoiler syntax (`||text||`) is always enabled. Any double-pipe delimiters in your content will be parsed as spoilers — for example, `a || b || c` would render `b` as a spoiler span rather than plain text.
+
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