add testing from master branch

docs/general/testing/web/index.md

@@ -16,3 +16,49 @@ Each PR of Jellyfin Web is automatically deployed to Cloudflare Pages. Please fo
    ![CF Pages Comment](/images/docs/testing/web/cf-pages-comment)
 3. Clicking on the link in the comment will open an instance of Jellyfin Web that is linked to a development instance of a Jellyfin demo server. You can login to the demo server with the credentials provided on the login page, or login to a different server by clicking `Change Server`.
 
+## Testing from source code
+
+Jellfin Web can be hosted as a standalone application without being associated to a Jellyfin server. In that case, a separate Jellyfin server will need to be prepared.
+
+"Test server" below refers to the device hosting Jellyfin web in the test setup.
+
+### Prerequisites
+
+Below are a list of things to prepare before testing Jellyfin web
+
+- Have an instance of Jellyfin Server.
+- Install [NodeJS, npm and nvm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) on the test server.
+- Install [git](https://github.com/git-guides/install-git) on the test server.
+- (Optional) Install [Github CLI](https://cli.github.com/) or [Github Desktop](https://github.com/apps/desktop) on the test server
+
+### Obtaining Jellyfin Web
+
+The Jellyfin Web source code can simply be cloned from the Github repository.
+Instructions on how to do so can be found [here](https://docs.github.com/en/repositories/creating-and-managing-repositories/cloning-a-repository).
+
+### Checking out branches
+
+The `master` branch is where the unstable build is built from. If you wish to test over there, please checkout that branch. to checkout the `master` branch, simply do the following.
+
+- Git CLI, Github CLI: open a terminal in the web folder and run `git checkout master`.
+- Github Desktop: Select the `master` branch in the branch dropdown menu.
+
+### Checking out PRs
+
+PRs are special branches submitted by contributors with the goal of eventually being merged into `master`. To checkout a PR, please follow the instructions below.
+
+1. Find the PR you would like to checkout in [the list of open PRs](https://github.com/jellyfin/jellyfin-web/pulls).
+2. Checkout the PR. [Git CLI and Github CLI](https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally), [Github Desktop](https://docs.github.com/en/desktop/working-with-your-remote-repository-on-github-or-github-enterprise/viewing-a-pull-request-in-github-desktop)
+
+### Install Dependencies
+
+1. Navigate to the web directory (the folder containing the cloned contents of the repository)
+2. Open a terminal window in the folder.
+3. run `npm install` to install prerequisites. This will need to be done every time you switch to a new branch.
+
+### Start Development Server
+
+1. Open a terminal window in the folder
+2. run `npm start` to start a development server. The server will start on port 8080. The server will auto update if the contents of the folder is changed.
+3. Connect devices to this server to start testing.
+4. Press `Ctrl+C` in the terminal window to stop the server.