Makefile and INSTALL doc changes

INSTALL.linux-static

@@ -0,0 +1,33 @@
+Compile on older container to get binary that runs on older OS too (SDL doesn't compile on older than 20.04):
+docker run -v .:/SDLRousku -it --rm ubuntu:20.04
+  On Linux, install the packages listed at
+  https://github.com/libsdl-org/SDL/blob/main/docs/README-linux.md#build-dependencies
+
+in addition apt install xdd nasm libwayland-dev
+
+mkdir vendored
+cd vendored
+git clone https://github.com/libsdl-org/SDL.git
+cd SDL
+cmake -S . -B build -DBUILD_SHARED_LIBS=OFF
+cmake --build build
+
+git clone https://github.com/libsdl-org/SDL_image.git
+cd SDL_image/external
+./download.sh
+cd ..
+cmake -S . -B build -DBUILD_SHARED_LIBS=OFF -DSDLIMAGE_VENDORED=ON -DCMAKE_PREFIX_PATH=../SDL/build
+cmake --build build
+
+git clone https://github.com/libsdl-org/SDL_ttf.git
+cd SDL_ttf/external/
+./download.sh
+cd ..
+cmake -S . -B build -DBUILD_SHARED_LIBS=OFF -DSDLTTF_VENDORED=ON  -DCMAKE_PREFIX_PATH=../SDL/build
+cmake --build build
+
+
+
+AppImage:
+make install DESTDIR=AppDir
+appimage-builder