dexc-desktop: add build doc for darwin (#2476)

Signed-off-by: Philemon Ukane <[email protected]>

client/cmd/dexc-desktop/README.md

@@ -1,7 +1,18 @@
+# Build Instructions for dexc-desktop
+
+The dexc-desktop client is a cross-platform desktop application for the DEX client and wallet. The instructions below are for building the client from source. If you are looking for pre-built binaries, see the [releases page](https://github.com/decred/dcrdex/releases).
+
+**Note**: The instructions below are to be run in your CLI from the `dexc-desktop` directory.
+
 ## Debian
-Build with `./debian-package.sh`. The deb archive is located in **./build**.
+Build with `./pkg/pkg-debian.sh`. The deb archive is located in **./build**.
 
 For development, you'll need to install the WebKit Development Libraries.
 `apt install libgtk-3-dev libwebkit2gtk-4.0-dev`
 For production, they are specified as DEPENDS in the control file and the
 package manager will install them.
+
+## MacOS (darwin)
+Build with `./pkg/pkg-darwin.sh` for `amd64` MacOS machines. If running on an
+`arm64` machine, you'll need to build with `TARGETS=darwin/arm64 ./pkg/pkg-darwin.sh` instead.
+The `.dmg` click installer can be located in **./pkg/installers** after a successful build.