README.md in zold-0.10.12 vs README.md in zold-0.10.13

- old
+ new

@@ -25,17 +25,13 @@
 
 ## How to Use
 
 First, install [Ruby 2.3+](https://www.ruby-lang.org/en/documentation/installation/),
 [Rubygems](https://rubygems.org/pages/download), and
-the [gem](https://rubygems.org/gems/zold):
+the [gem](https://rubygems.org/gems/zold).
+Here is [how](https://github.com/yegor256/zold/blob/master/INSTALL.md).
 
-```bash
-$ sudo apt-get install ruby-dev rubygems zlib1g-dev libssl-dev
-$ gem install zold
-```
-
 To make sure it's installed, try:
 
 ```bash
 $ zold --help
 ```
@@ -96,10 +92,12 @@
 
 ```bash
 $ zold node --trace --verbose --invoice=5f96e731e48ae21f --host=4.4.4.4
 ```
 
-Then, open the page `4.4.4.4:4096` in your browser.
+Then, open the page `4.4.4.4:4096` in your browser
+(you may need to open the inbound port at your
+[IP firewall](https://www.howtogeek.com/177621/the-beginners-guide-to-iptables-the-linux-firewall/)).
 If you see a simple JSON document, everything is fine.
 Next, hit <kbd>Ctrl</kbd>+<kbd>c</kbd> and run this line, in order
 to start the node and make sure it will be online even when you log off
 (replace `CMD` with the command you just executed before):
 