Update installation instructions for debian (#1373)

Author: isidentical

docs/README.md

@@ -162,6 +162,8 @@ Also works for other Debian-derived distributions like MX Linux, Linux Mint, dee
 
 ```bash
 # Install httpie
+$ curl -SsL https://packages.httpie.io/deb/KEY.gpg | apt-key add -
+$ curl -SsL -o /etc/apt/sources.list.d/httpie.list https://packages.httpie.io/deb/httpie.list
 $ apt update
 $ apt install httpie
 ```

docs/installation/methods.yml

@@ -36,6 +36,8 @@ tools:
       package: https://packages.debian.org/sid/web/httpie
     commands:
       install:
+        - curl -SsL https://packages.httpie.io/deb/KEY.gpg | apt-key add -
+        - curl -SsL -o /etc/apt/sources.list.d/httpie.list https://packages.httpie.io/deb/httpie.list
         - apt update
         - apt install httpie
       upgrade: