add example

example/subscribe.js

@@ -0,0 +1,18 @@
+const ElectrumClient = require('..')
+const sleep = (ms) => new Promise((resolve,_) => setTimeout(() => resolve(ms), ms))
+
+const main = async () => {
+    const ecl = new ElectrumClient(995, 'btc.smsys.me', 'tls')
+    ecl.subscribe.on('server.peers.subscribe', console.log)
+    ecl.subscribe.on('blockchain.numblocks.subscribe', console.log)
+    ecl.subscribe.on('blockchain.headers.subscribe', console.log)
+    await ecl.connect()
+    const p1 = await ecl.serverPeers_subscribe()
+    const p2 = await ecl.blockchainHeaders_subscribe()
+    const p3 = await ecl.blockchainNumblocks_subscribe()
+    while(true){
+        await sleep(1000)
+    }
+    await ecl.close()
+}
+main()