From QGIS Plugin Manager

To install the plugin, you can simply use QGIS Plugin Manager. In your QGIS, click Plugin menu and Manage and Install Plugins... After the Plugin Installer dialog shows up, search for QGIS Resources Sharing in the search box of the dialog in the All tab. Select the QGIS Resources Sharing plugin and click Install

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From the repository

If you are adventurous and would like to get the latest code of the plugin, you can install it directly from the repository. The repository is in Github here. There are 2 ways that you can do generally:

  • Download the zip from github here: ZIP Master, extract the zip, and copy the extracted root directory into QGIS local plugins directory (on Linux it’s ~/.qgis2/python/plugins, on Windows it’s C:\Users\{username}\.qgis2\python\plugins)

  • Use git: clone the repository in that directory or clone in your preferred location and use symbolic link in local plugins directory.