Add a bit of documentation to build using vcpkg Linux

INSTALL.md

@@ -23,6 +23,7 @@ Building QGIS from source - step by step
       + [3.11.2. Suggested system tweaks](#3112-suggested-system-tweaks)
       + [3.11.3. Additional tools for QGIS development](#3113-additional-tools-for-qgis-development)
       + [3.11.4. QT6 experimental builds with Fedora Rawhide](#3114-qt6-experimental-builds-with-fedora-rawhide)
+   * [3.12. Building on Linux with vcpkg](#52-building--on-linux-with-vcpkg)
 - [4. Building on Windows](#4-building-on-windows)
    * [4.1. Building with Microsoft Visual Studio](#41-building-with-microsoft-visual-studio)
       + [4.1.1. Visual Studio 2022 Community Edition](#411-visual-studio-2022-community-edition)
@@ -581,6 +582,49 @@ To build,
 cmake .. -DBUILD_WITH_QT6=ON -DWITH_QTWEBKIT=OFF -DWITH_QTWEBENGINE=ON
 ```
 
+## 3.12. Building on Linux with vcpkg
+
+With [vcpkg](https://github.com/microsoft/vcpkg/) you can develop QGIS using
+Qt6 on a Linux system.
+
+Install and initialize vcpkg
+
+```sh
+export VCPKG_ROOT=$HOME/.vcpkg
+wget https://aka.ms/vcpkg-init.sh -O /tmp/vcpkg-init.sh
+. /tmp/vcpkg-init.sh
+```
+
+Get the QGIS source code
+
+```sh
+git clone [email protected]:qgis/QGIS.git
+```
+
+Configure
+
+```sh
+cmake -S . \
+      -B ./build-x64-linux \
+      -GNinja \
+      -DCMAKE_BUILD_TYPE=Debug \
+      -DWITH_VCPKG=ON \
+      -DBUILD_WITH_QT6=ON \
+      -DWITH_QTWEBKIT=OFF \
+      -DWITH_BINDINGS=ON \
+      -DVCPKG_TARGET_TRIPLET=x64-linux-dynamic-release \
+      -DVCPKG_HOST_TRIPLET=x64-linux-dynamic-release
+```
+
+Build
+
+```sh
+cmake --build ./build-x64-linux
+```
+
+We assume that you have the source code of QGIS ready and created a
+new subdirectory called `build-x64-linux`.
+
 # 4. Building on Windows
 
 ## 4.1. Building with Microsoft Visual Studio