document How to make live reload work in Rollup based projects like Svelte.

Fixes gitpod-io/website#770

Author: nisarhassan12

src/docs/languages/javascript.md

@@ -69,6 +69,33 @@ and then search for `eslint` in the extensions tab and then install it from ther
 
 ![Install Eslint in Gitpod](../images/eslint-extension.png)
 
+## Making Live Reload work in Rollup based projects like Svelte
+
+If your porject uses Rollup as a module bundler then in order for live reload to work in Gitpod you'll have to add a bit of configuration as specified below:
+
+- Setup an environment variable called `CLIENT_URL` in the `.gitpod.yml` config file as shown below please make sure that you set it up before the task which starts the dev server(which is `npm run dev` in this case):
+
+  ```bash
+  - init: npm install
+      command: |
+        export CLIENT_URL="$(gp url 35729)/livereload.js?snipver=1&port=443"
+        npm run dev
+  ```
+
+- Pass the value of `CLIENT_URL` environment variable to the `rollup-plugin-livereload` in `rollup-config.js` inside of the `plugins` array as shown:
+  ```js
+  plugins: [
+    !production &&
+      livereload({
+        watch: 'public',
+        clientUrl: process.env.CLIENT_URL
+      })
+  ]
+  ```
+  This will set `CLIENT_URL` to the workspace url of port `35729` (default port for livereload in Gitpod).
+
+https://github.com/gitpod-io/sveltejs-template repo is a working example of the config described above <span aria-hidden="true">👆</span>.
+
 ## Further Reading
 
 - [Sustainable Node.js development with only a browser](/blog/node-js-development/).