Update README.md

Fix downloading pk2appimage binary. The original snippet was pointing to the HTML releases page, which doesn't contain the releases anymore (that page loads them using JavaScript). Retrieving the download URL from GitHub's API should be more reliable and future proof.

Author: ivanvc

README.md

@@ -15,7 +15,7 @@ Some branded applications are unfortunately not provided in AppImage format by t
 For applications for which there is already an existing [`.yml` recipe file](../../tree/master/recipes), you can simply use the name of the application (without `.yml`) as an argument. For example, to produce a Spotify AppImage, it is sufficient to do:
 
 ```
-wget -c https://github.com/$(wget -q https://github.com/AppImage/pkg2appimage/releases -O - | grep "pkg2appimage-.*-x86_64.AppImage" | head -n 1 | cut -d '"' -f 2)
+wget -c $(wget -q https://api.github.com/repos/AppImageCommunity/pkg2appimage/releases -O - | grep "pkg2appimage-.*-x86_64.AppImage" | grep browser_download_url | head -n 1 | cut -d '"' -f 4)
 chmod +x ./pkg2appimage-*.AppImage
 ./pkg2appimage-*.AppImage Spotify
 ```
@@ -25,7 +25,7 @@ chmod +x ./pkg2appimage-*.AppImage
 To build an AppImage from a local `.yml` recipe (e.g., during development):
 
 ```
-wget -c https://github.com/$(wget -q https://github.com/AppImage/pkg2appimage/releases -O - | grep "pkg2appimage-.*-x86_64.AppImage" | head -n 1 | cut -d '"' -f 2)
+wget -c $(wget -q https://api.github.com/repos/AppImageCommunity/pkg2appimage/releases -O - | grep "pkg2appimage-.*-x86_64.AppImage" | grep browser_download_url | head -n 1 | cut -d '"' -f 4)
 chmod +x ./pkg2appimage-*.AppImage
 ./pkg2appimage-*.AppImage recipes/XXX.yml
 ```