updated theme Twenty Nineteen version 2.9

wp-content/themes/twentynineteen/contributing.txt

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+=== Contributing to Twenty Nineteen ===
+
+= Compiling SCSS =
+
+Twenty Nineteen relies on Sass, which allows us to more easily share code between multiple stylesheets (style.css, style-editor.css, etc.). To compile Sass files (.scss), use the built-in npm build tool. The build tool will make sure that your compiled CSS code stays in sync and has the correct formatting.
+
+Installation instructions
+
+1. Using a command line interface, go to the “twentynineteen” directory `cd /my-computer/local-wordpress-install/src/wp-content/themes/twentynineteen`.
+
+2. Type `npm install` into the command line, and press the [return] key, to install all Node.js dependencies.
+
+3. The dependencies may take a few minutes to download but once it completes, you’re done.
+
+Usage instructions
+
+1. After making a change to a .scss file, run `npm run build` from within the theme directory to build the CSS files with your new changes. You may need to run the build command twice to update style-rtl.css (because the RTL process might update from style.css before that is updated from Sass file changes).
+
+2. You can also “watch” the theme directory for Sass changes and rebuild the CSS anytime a change occurs by running: `npm run watch`.