Add instructions for getting make to work on Windows

CONTRIBUTING.md

@@ -7,6 +7,8 @@ When preparing a PR here are some general guidelines:
 - To test your changes before submission, run `make` at the top level,
   which will generate all required `Everything` files in
   `Cubical/README.agda` and then typecheck the latter file.
+  If you're using Windows, [here](MAKEWINDOWS.md) are some instructions
+  to get the `make` command working.
 
 - Please read through and clean your code before making a PR. Clean
   code has reasonable line length (<100 characters), good indentation,

MAKEWINDOWS.md

@@ -0,0 +1,32 @@
+# Instructions for getting `make` to work on Windows
+
+The GNU command `make` does not work out of the box on Windows.
+Here are some steps you could take to get `make` working on a Windows machine:
+
+1.  You probably already installed the Chocolatey package manager when
+    installing Agda (check by running `choco` in terminal). If not, install it
+    from [here](https://chocolatey.org/install).
+
+2.  You need to install the `make` command by running
+    ```
+    choco install make
+    ```
+
+3.  The [makefile](GNUmakefile) runs the `runhaskell` command, which might not
+    work on your system. Test this by running in terminal
+    ```
+    runhaskell
+    ```
+    If that doesn't work, create a file called `runhaskell.bat` with the contents
+    ```
+    runghc %*
+    ```
+    and put this somewhere in your PATH.
+
+4.  Give your user account `Read & Execute` access to `C:\Windows\System32\pthread.dll`
+
+5.  Now, **each time before you run `make`,** run the following command in your terminal:
+    ```
+    chcp.com 65001
+    ```
+    so that Haskell can parse UTF-8 characters.