Add systemd-devel for Fedora Linux dependencies (#528)

It is required for the dependency crate libudev-sys (error about missing libudev.pc)

docs/linux_dependencies.md

@@ -11,7 +11,7 @@ sudo apt-get install pkg-config libx11-dev libasound2-dev libudev-dev
 
 ## Fedora 32
 ```bash
-sudo dnf install gcc-c++ libX11-devel alsa-lib-devel
+sudo dnf install gcc-c++ libX11-devel alsa-lib-devel systemd-devel
 ```
 
 ## Arch / Manjaro
@@ -70,4 +70,4 @@ At this point, projects should successfully compile but fail on execution. This
 1. `find target -type f -name glslang_validator` in order to find glslang_validator in `target/debug/build/bevy-glsl-to-spirv-<hash>/out/glslang_validator`. The directory containing glslang_validator will be referenced again, so save it for later: `export OUT_DIR="$(dirname $(find target -type f -name glslang_validator))"`.
 2. Running `ldd $OUT_DIR/glslang_validator` may show `libstdc++.so.6` is not found. If all dependencies are found, then bevy should work. If not, install (globally or in nix-shell) any of the results found by `nix-locate -w libstdc++.so.6`. For example purposes, consider `nixos.gcc-unwrapped`. In theory, any of the ones in `find -L /nix/store -type f -name libstdc++.so.6` will work.
 3. `patchelf --set-interpreter "$(cat $NIX_CC/nix-support/dynamic-linker)" --set-rpath /nix/store/784rh7jrfhagbkydjfrv68h9x3g4gqmk-gcc-8.3.0-lib/lib $OUT_DIR/glslang_validator`
-4. Bevy should now be working properly!
+4. Bevy should now be working properly!