Fix Debian install instructions

docs/install.md

@@ -65,9 +65,10 @@ Installation via Debian repository:
 
 === "x86_64/amd64"
     ```bash
-    curl -sSL https://archive.heckel.io/apt/pubkey.txt | sudo apt-key add -
+    sudo mkdir -p /etc/apt/keyrings
+    curl -fsSL https://archive.heckel.io/apt/pubkey.txt | sudo gpg --dearmor -o /etc/apt/keyrings/heckel.io.gpg
     sudo apt install apt-transport-https
-    sudo sh -c "echo 'deb [arch=amd64] https://archive.heckel.io/apt debian main' \
+    sudo sh -c "echo 'deb [arch=amd64 signed-by=/etc/apt/keyrings/heckel.io.gpg] https://archive.heckel.io/apt debian main' \
         > /etc/apt/sources.list.d/archive.heckel.io.list"  
     sudo apt update
     sudo apt install ntfy

docs/releases.md

@@ -20,6 +20,7 @@ and the [ntfy Android app](https://github.com/binwiederhier/ntfy-android/release
 * Updated developer docs, bump nodejs and go version ([#414](https://github.com/binwiederhier/ntfy/issues/414), thanks to [@YJSoft](https://github.com/YJSoft) for reporting)
 * Officially document `?auth=..` query parameter ([#433](https://github.com/binwiederhier/ntfy/pull/433), thanks to [@wunter8](https://github.com/wunter8))
 * Added Rundeck example ([#427](https://github.com/binwiederhier/ntfy/pull/427), thanks to [@demogorgonz](https://github.com/demogorgonz))
+* Fix Debian installation instructions ([#237](https://github.com/binwiederhier/ntfy/issues/237), thanks to [@Joeharrison94](https://github.com/Joeharrison94) for reporting)
 
 **Additional translations:**