Added build with Docker

Dockerfile

@@ -0,0 +1,28 @@
+FROM vitasdk/vitasdk:latest
+
+RUN apk add --no-cache \
+    cmake \
+    make \
+    git \
+    ca-certificates
+
+# vdpm is pre-installed at /usr/local/vitasdk/bin/vdpm
+# -f = force install (also works for first-time installs)
+RUN vdpm -f \
+    zlib \
+    libpng \
+    libjpeg-turbo \
+    freetype \
+    openssl \
+    curl \
+    zstd \
+    vita2d
+
+WORKDIR /src
+COPY . .
+
+RUN cmake -B /build -DCMAKE_BUILD_TYPE=Release . && \
+    cmake --build /build --parallel "$(nproc)"
+
+# Mount a host directory to /output to retrieve the VPK
+CMD ["sh", "-c", "cp /build/vitaImmich.vpk /output/vitaImmich.vpk && echo 'Done: /output/vitaImmich.vpk'"]