add warning for find_word

src/language/mod.rs

@@ -167,6 +167,10 @@ impl Language {
 	}
 
 	/// Get the index of the word in the word list.
+	///
+	/// WARNING: indices returned by this function start with `0`,
+	/// while indices start with `1` in a lookup against [BIP39 on github](https://github.com/bitcoin/bips/blob/master/bip-0039/english.txt) (and most wallet docs).
+	/// In other words `find_word("abandon")` returns `Some(0)` instead of `Some(1)` (which a naive user could assume).
 	#[inline]
 	pub fn find_word(self, word: &str) -> Option<u16> {
 		match self {