Add Zig implementation

zig/README.md

@@ -0,0 +1,34 @@
+# Gilded Rose starting position in Zig
+
+I assume you have [installed](https://ziglang.org/learn/getting-started/#installing-zig) `zig` on your system.
+
+## Run unit tests from the command line
+
+```sh
+$ zig build test
+```
+
+## Run the TextTest fixture on the command line
+
+Build and install the executable
+
+```sh
+$ zig build
+```
+
+Execute it on the command line with an argument for the number of days:
+
+```sh
+$ ./zig/zig-out/bin/zig 10
+```
+
+## Run the TextTest approval test that comes with this project
+
+There are instructions in the [TextTest Readme](../texttests/README.md) for setting up TextTest.
+You will need to specify the executable in [config.gr](../texttests/config.gr).
+Uncomment this line to use it:
+
+```
+#executable:${TEXTTEST_HOME}/zig/zig-out/bin/zig
+```
+