Document scratch-gui STATIC_PATH build parameter

Author: Christopher Willis-Ford

README.md

@@ -11,12 +11,19 @@ that repository's main development line. For now, though, there's a separate bra
 
 1. Clone the `scratch-gui` repository if you haven't already.
 2. Switch to the `scratch-desktop` branch with `git checkout scratch-desktop`
-3. Build with `BUILD_MODE=dist`:
-   - macOS, WSL, or Cygwin: run `BUILD_MODE=dist npm run build` or `BUILD_MODE=dist npm run watch`
-   - CMD: run `set BUILD_MODE=dist` once, then `npm run build` or `npm run watch` any number of times in the same
+3. Build with `BUILD_MODE=dist` and `STATIC_PATH=static`:
+   - macOS, WSL, or Cygwin: run `BUILD_MODE=dist STATIC_PATH=static npm run build` or
+     `BUILD_MODE=dist STATIC_PATH=static npm run watch`
+     - Running `npm run build-gui` in `scratch-desktop` is a shortcut for this when using `npm link`.
+   - CMD: run `set BUILD_MODE=dist` once and `set STATIC_PATH=static` once, then `npm run build` or `npm run watch`
+     any number of times in the same
      window.
-   - PowerShell: run `$env:BUILD_MODE = "dist"` once, then `npm run build` or `npm run watch` any number of times in
-     the same window.
+   - PowerShell: run `$env:BUILD_MODE = "dist"` once and `$env:STATIC_PATH = "static"` once, then `npm run build` or
+     `npm run watch` any number of times in the same window.
+
+If you have run `npm link scratch-gui` (or equivalent) in the `scratch-desktop` working directory, you may be able to
+accomplish the above by running `npm run build-gui` in the `scratch-desktop` directory instead of using the manual
+steps listed above.
 
 ### Prepare media library assets
 

package.json

@@ -7,6 +7,7 @@
   "license": "BSD-3-Clause",
   "scripts": {
     "start": "electron-webpack dev --bail --display-error-details --env.minify=false",
+    "build-gui": "cd ./node_modules/scratch-gui && BUILD_MODE=dist STATIC_PATH=static npm run build",
     "clean": "rimraf ./dist/ ./static/assets/",
     "compile": "rimraf ./dist/ && electron-webpack --bail --display-error-details --env.minify=false",
     "fetch": "rimraf ./static/assets/ && mkdirp ./static/assets/ && node ./scripts/fetchMediaLibraryAssets.js",