Update installation instructions

Author: ubruhin

modules/installation/pages/linux.adoc

@@ -35,6 +35,15 @@ If you're not familiar with the terminal: Right-click on the downloaded file
 and then check something like _Allow executing file as program_ or
 _Run as executable_. Afterwards double-click the file to run it.
 
+[NOTE]
+====
+If LibrePCB silently doesn't start, run the AppImage from a terminal to see any
+error messages. It is possible that you need to install some system libraries.
+
+Especially from Ubuntu 26.04 onwards, it seems that OpenGL needs to be installed
+in order to get LibrePCB functional: `sudo apt install libglu1-mesa`
+====
+
 [#snap,reftext=Snap Package]
 == Snap Package (multi-arch)
 

modules/installation/pages/macos.adoc

@@ -16,22 +16,10 @@ Double-click the downloaded file in Finder. Then drag and drop the LibrePCB
 app onto the "Applications" folder in Finder. Afterwards you'll find
 LibrePCB in the Launchpad.
 
-[IMPORTANT]
+[NOTE]
 ====
-Unfortunately we're not able (yet) to officially sign the macOS binary.
-Therefore macOS refuses to start LibrePCB by default. As a workaround,
-you need to run it once with menu:Right-click[Open] on the LibrePCB
-application in the Launchpad. If this doesn't work, try it a second time.
-
-Afterwards you should be able to run LibrePCB normally with a single click.
+Starting from LibrePCB 2.x, our official releases are signed by
+*Scheibling Consulting AB* as you may see when running LibrePCB the first time.
+This code signing service is thankfully sponsored by
+https://ossign.org/[OSSign].
 ====
-
-// Keep this section just for some time to keep the links working and to
-// inform users about the change.
-[#online-installer,reftext=Online Installer]
-== Online Installer (abandoned)
-
-Note that starting with LibrePCB 1.0, we do no longer provide an installer for
-macOS. If you installed a previous LibrePCB release with the installer,
-please uninstall it with the _LibrePCB Maintenance Tool_ and install the
-latest release with the <<portable-package>> instead.

modules/installation/pages/windows.adoc

@@ -13,6 +13,14 @@ Afterwards you'll find LibrePCB in your start menu.
 
 [NOTE]
 ====
+Starting from LibrePCB 2.0, our official releases are signed by
+*Scheibling Consulting AB* as you may see when running LibrePCB the first time.
+This code signing service is thankfully sponsored by
+https://ossign.org/[OSSign].
+====
+
+[TIP]
+====
 For automated (unattended) installation, please check out the command-line
 parameters of the Inno Setup framework
 https://jrsoftware.org/ishelp/index.php?topic=setupcmdline[here]