add update guide for 1.7.1

UPDATE.md

@@ -1,3 +1,21 @@
+## 1.7.0 -> 1.7.1
+pull the update: `git pull`  
+make the following changes in your config.json file:
+```diff
+...
+	"antispam": {
+		...
+	},
++	"ntfy": {
++		"enabled": false,
++		"host": "https://ntfy.sh",
++		"user": "",
++		"pass": "",
++		"topic": ""
++	},
+...
+```
+
 ## 1.6.x -> 1.7.0
 pull the update: `git pull`  
 run `pip install -r requirements.txt` again to install newly required packages