Added README and command line argument functionality

content/_code-samples/key-derivation/js/README.md

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+# JavaScript key derivation examples
+
+Generates key from a given input in Ed25519 and Secp256k1 format
+
+## Command-line usage:
+
+### Password like seed    
+
+    npm start "sEdSKaCy2JT7JaM7v95H9SxkhP9wS2r"
+
+### Rippled RFC1751 Mnemonic
+
+    npm start "KANT FISH GENE COST WEB JAKE CHUM HAD SOD MID KICK BOTH"
+
+### Hex formatted seed
+
+    npm start "0x21edc3dec3ef1873cf8f333381c5f360c3"
+
+### Random seed
+
+    npm start