Update README.md

add TODO entry about `bitcoinAddress`

Author: Lucien Grondin

README.md

@@ -416,7 +416,7 @@ You can specify an optional index :
 * [x] use [Jacobian coordinates](https://en.wikibooks.org/wiki/Cryptography/Prime_Curve/Jacobian_Coordinates)
 * [ ] use a better exponentiation method, for instance using precomputations
 * [ ] always output public keys in ASCII, and private keys in binary
-
+* [ ] get `bitcoinAddress` to generate various addresses from extended keys, picking an appropriate derivation path.
 
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