fix zig fetch command in README (#130)

* fix zig fetch command in README

All URLs within build.zig.zon files must point to archives that never
change.  However, the zig fetch command in the README.md adds a URL
that points to the `devel` git branch whose content changes whenever
the `devel` branch is updated.

I've updated the README a url that zig will resolve to a SHA before it
writes it to the zon file.

* Update template scripts

---------

Co-authored-by: Not-Nik <nik.wipper@gmx.de>

project_setup.sh

@@ -57,20 +57,16 @@ pub fn build(b: *std.Build) !void {
     b.installArtifact(exe);
 }' >> build.zig
 
-HASH=$(zig fetch https://github.com/Not-Nik/raylib-zig/archive/devel.tar.gz)
-
 echo '.{
     .name = "'$PROJECT_NAME'",
     .version = "0.0.1",
     .dependencies = .{
-        .@"raylib-zig" = .{
-            .url = "https://github.com/Not-Nik/raylib-zig/archive/devel.tar.gz",
-            .hash = "'$HASH'",
-        },
     },
     .paths = .{""},
 }' >> build.zig.zon
 
+zig fetch --save git+https://github.com/Not-Nik/raylib-zig#devel
+
 mkdir src
 mkdir resources
 touch resources/placeholder.txt