Added installation links to README.md

Also included links to SignPath regarding their free code signing service.

Closes #3691

README.md

@@ -18,16 +18,28 @@ be used in any map. Tilesets can be modified at any time.
 [![Translation status](https://hosted.weblate.org/widgets/tiled/-/shields-badge.svg)](https://hosted.weblate.org/engage/tiled/?utm_source=widget)
 [![Open Source Helpers](https://www.codetriage.com/mapeditor/tiled/badges/users.svg)](https://www.codetriage.com/mapeditor/tiled)
 
-About the Qt Version
+Installing Tiled
 -------------------------------------------------------------------------------
 
-Tiled was originally written in Java. In 2008, work began to develop a faster,
-better looking, and easier-to-use version of Tiled based on the Qt framework.
-This decision was made as the Qt framework has a greater feature set than is
-offered by the standard Java libraries.
+Tiled is available for all major operating systems and can be downloaded either
+from [GitHub Releases](https://github.com/mapeditor/tiled/releases) or from
+[itch.io](https://thorbjorn.itch.io/tiled). Most Linux distributions also
+package Tiled, but these packages are usually out of date so you might prefer
+to use the AppImage or install Tiled through
+[Flatpak](https://flathub.org/apps/org.mapeditor.Tiled) or
+[snap](https://snapcraft.io/tiled), both of which are official releases.
 
+### Signed Releases for macOS and Windows
 
-Compiling
+macOS builds are signed by the maintainer, Thorbjørn Lindeijer, who registered
+as Apple Developer.
+
+Windows installers are using free code signing provided by
+[SignPath.io](https://signpath.io?utm_source=foundation&utm_medium=github&utm_campaign=tiled),
+and a free code signing certificate by the
+[SignPath Foundation](https://signpath.org?utm_source=foundation&utm_medium=github&utm_campaign=tiled).
+
+Compiling Tiled
 -------------------------------------------------------------------------------
 
 Before you can compile Tiled, you must ensure the Qt (>= 5.12) development
@@ -69,10 +81,10 @@ You can now run Tiled as follows:
 
     qbs run -p tiled
 
-Qt 6
--------------------------------------------------------------------------------
+### Qt 6
 
-For compiling libtiledquick you'll need to install the Vulkan headers:
+For compiling libtiledquick (not built by default) you'll need to install the
+Vulkan headers:
 
 * On Ubuntu/Debian: `sudo apt install libvulkan-dev`
 
@@ -84,7 +96,7 @@ using that IDE. This can be done with the following command:
 
     qbs generate -g visualstudio2017
 
-Installing
+Installing Self-Compiled Tiled
 -------------------------------------------------------------------------------
 
 To install Tiled, run `qbs install` from the terminal. By default, Tiled will