Add simple README for Linux packages

package.json

@@ -76,7 +76,7 @@
         },
         {
           "from": "resources/linux",
-          "filter": "create_desktop_file.sh"
+          "filter": ["create_desktop_file.sh", "README.md"]
         }
       ]
     },

resources/linux/README.md

@@ -0,0 +1,74 @@
+# Mattermost Desktop for Linux
+
+## Table of Contents
+
+- [Install](#install)
+- [Usage](#usage)
+- [Contributing](#contributing)
+- [License](#license)
+
+
+## Install
+
+If you were installed the application via package managers, you don't have to do
+anymore. It's ready to use in your system, so please follow [usage](#usage)
+instruction.
+
+First, locate the extracted directory into your desired directory (e.g.
+`/opt/mattermost-desktop-<VERSION>`).
+
+
+### Desktop launcher
+
+Execute the script file to create `Mattermost.desktop` file.
+
+```
+/opt/mattermost-desktop-<VERSION>/create_desktop_file.sh
+```
+
+Then move it into appropreate directory of your desktop environment. For
+example, it's `~/.local/share/applications/` for current user on Ubuntu Unity.
+
+```
+mv Mattermost.desktop ~/.local/share/applications/
+```
+
+### Terminal command
+
+Set `PATH` environment variable to enable launching from terminal.
+For example, you can append following line into `~/.bashrc`.
+
+```sh
+# assuming that /opt/mattermost-desktop-<VERSION>/mattermost-desktop is the executable file.
+export PATH=$PATH:/opt/mattermost-desktop-<VERSION>
+```
+
+Alternatively, you can also create a symbolic link for the application.
+
+```sh
+sudo ln -s /opt/mattermost-desktop-<VERSION>/mattermost-desktop /usr/local/bin/
+```
+
+## Usage
+
+After launching, you need to configure the application to interact with your team.
+
+1. If you don't see "Settings" page, select **File** -> **Settings...** from the menu bar.
+2. Click **Add new team** next to the right of Team Management section.
+3. Enter **Name** and a valid **URL**, which begins with either `http://` or `https://`.
+4. Click **Add**.
+
+
+### More guides
+
+Available at [Mattermost Documentation](https://docs.mattermost.com/help/apps/desktop-guide.html).
+
+
+## Contributing
+
+See [the contribute file](https://github.com/mattermost/desktop/blob/master/CONTRIBUTING.md).
+
+
+## License
+
+Apache Lisence, Version 2.0