Add instructions for manual registration of a new npm version

Author: aminya

CONTRIBUTING.md

@@ -0,0 +1,23 @@
+## Releasing a new npm version
+
+- Change the version in `package.json`, make a new git tag, and push it to GitHub.
+- Wait until the GitHub Actions on the master branch pass.
+- The artifacts of the latest GitHub Action run should be downloaded from the actions tab of the GitHub repository
+- The artifacts.zip should be extracted and placed under the `prebuilds` folder (replacing the old folder if it exists).
+
+	The `prebuilds` folder should look like the following.
+	```
+	repository-root
+		|-prebuilds
+			 |_linux-x64
+	  		 |...
+			 |_darwin-x64
+				 |...
+			 |_win32-x64
+				 |...
+	```
+
+- Then:
+	```
+	npm publish
+	```