add rss icon in sidebar media selection

[gadore]

因为这个主题暂时没有设置Rss显示的地址，我对这个又比较看重，所以就在社交媒体里边增加了一个Rss选择的图标选项，已测试，显示正常，可通过我的博客地址预览显示效果https://gadore.top

None

[f2c-ci-robot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ruibaby

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[ruibaby]

Nice Work!