Doc:Install or build>Build>Unix>Install third-party software: Add instructions...

Doc:Install or build>Build>Unix>Install third-party software: Add instructions to install Qt via command line

hugo/content/installation/building/unix/third-party.md

@@ -127,3 +127,58 @@ BornAgain dependencies by running the following command:
 sudo port install git cmake fftw-3 gsl py3-matplotlib py3-numpy\
  tiff boost qt5-mac
 ```
+
+#### Minimal Qt installation via command line
+
+The Qt framework with arbitrary components can be installed via command line.
+To perform a minimal installation, first download a Qt installer for the platform
+from the official website.
+
+Remember to set up a Qt account beforehand; this is required for
+any installation.
+
+Define the following variables:
+* Path to the downloaded Qt installer
+  ```
+  qt_installer='/path/to/Qt-installer'
+  ```
+* Root path for Qt installation
+  ```
+  qt_root='/Qt/installation/path'
+  ```
+* Qt credentials
+  ```
+  qt_email='myemail@some.org'
+  qt_passw='myPassWord'
+  ```
+
+For a minimal Qt installation (only the components for gcc 64bit), use
+```
+$qt_installer --root "$qt_root" --email "$qt_email" --pw "$qt_passw" \
+  --auto-answer telemetry-question=No,AssociateCommonFiletypes=No --accept-licenses \
+  --no-default-installations install qt.qt6.623.gcc_64
+```
+where `qt.qt6.623.gcc_64` is the name of the component to install.
+
+Note that during the installation some questions must be answered
+(e.g. with `Accept` or `Yes`).
+
+For searching Qt components (e.g. search for Qt6 components `qt.qt6`), use
+```
+$qt_installer --email "$qt_email" --pw "$qt_passw" search qt.qt6
+```
+
+After the installation, under the Qt root directory one finds the
+detailed installation log, `InstallationLog.txt`,
+and Qt maintenance tool, `MaintenanceTool`.
+
+Qt maintenance tool can be used to remove or update components;
+e.g. for removing Qt Creator, use
+```
+$qt_root/MaintenanceTool remove qt.tools.qtcreator
+```
+
+For further information, see the official guide to the Qt-installer
+command-line interface:
+* <https://doc.qt.io/qtinstallerframework/ifw-cli.html>
+* <https://doc.qt.io/qtinstallerframework/ifw-use-cases-cli.html>