Add Arch Linux Docker build support

- Add Dockerfile.archlinux with all required Arch Linux build dependencies
- Update building.md with Docker build and test instructions for Arch Linux

Author: mfisher31

Dockerfile.archlinux

@@ -0,0 +1,40 @@
+# Dockerfile for building and testing Element on Arch Linux
+# This creates a build environment - mount your source code as a volume
+FROM archlinux:latest
+
+# Update system and install dependencies
+RUN pacman -Syu --noconfirm && \
+    pacman -S --noconfirm \
+        git \
+        base-devel \
+        cmake \
+        ninja \
+        pkgconf \
+        boost \
+        freetype2 \
+        fontconfig \
+        libx11 \
+        libxext \
+        libxrandr \
+        libxcomposite \
+        libxinerama \
+        libxrender \
+        libxcursor \
+        alsa-lib \
+        jack2 \
+        lv2 \
+        lilv \
+        suil \
+        ladspa \
+        curl \
+        ttf-roboto \
+        clang \
+        pandoc \
+        ccache && \
+    pacman -Scc --noconfirm
+
+# Set up working directory
+WORKDIR /workspace
+
+# Default command
+CMD ["/bin/bash"]

docs/building.md

@@ -38,6 +38,31 @@ sudo pacman -S git base-devel cmake ninja pkgconf boost \
     ladspa curl ttf-roboto clang
 ```
 
+### Checking With Docker
+
+You can also build in a Docker container without installing packages on your system:
+
+```bash
+# Build the Arch Linux environment image
+docker build -f Dockerfile.archlinux -t element:archlinux .
+
+# Build the project with your source mounted as a volume
+docker run --rm --user $(id -u):$(id -g) -v $(pwd):/workspace element:archlinux bash -c "
+  git config --global --add safe.directory /workspace && \
+  git submodule update --init --recursive && \
+  cmake -B build-arch -G Ninja -DCMAKE_BUILD_TYPE=Release -DELEMENT_BUILD_PLUGINS=ON && \
+  cmake --build build-arch && \
+  ctest --test-dir build-arch --output-on-failure
+"
+```
+
+Or run interactively:
+```bash
+docker run --rm -it --user $(id -u):$(id -g) -v $(pwd):/workspace element:archlinux
+# Then run cmake commands manually inside the container
+```
+
+
 ## Mac OSX
 __Dependencies__