add documentation link to ui (#146)

ErsatzTV/Shared/MainLayout.razor

@@ -29,6 +29,9 @@
         <MudLink Color="Color.Info" Href="/iptv/channels.m3u" Target="_blank" Underline="Underline.None">M3U</MudLink>
         <MudLink Color="Color.Info" Href="/iptv/xmltv.xml" Target="_blank" Class="mx-4" Underline="Underline.None">XMLTV</MudLink>
         <MudLink Color="Color.Info" Href="/swagger" Target="_blank" Class="mr-4" Underline="Underline.None">API</MudLink>
+        <MudTooltip Text="Documentation">
+            <MudIconButton Icon="@Icons.Material.Filled.Help" Color="Color.Primary" Link="https://ersatztv.org" Target="_blank"/>
+        </MudTooltip>
         <MudTooltip Text="Discord">
             <MudIconButton Icon="fab fa-discord" Color="Color.Primary" Link="https://discord.gg/hHaJm3yGy6" Target="_blank"/>
         </MudTooltip>