Add bisqJS and liquidJS npm modules.

examples/nodejs/mempool-js/bitcoin/difficulty.ts

@@ -0,0 +1,15 @@
+import mempoolJS from "./../../../../src/index";
+
+const init = async () => {
+  try {
+    const {
+      bitcoin: { difficulty },
+    } = mempoolJS();
+    
+    const difficultyAdjustment = await difficulty.getDifficultyAdjustment();
+    console.log(difficultyAdjustment);
+  } catch (error) {
+    console.log(error);
+  }
+};
+init();