概要

Rider の Preferences の「Editor > Live Templates > C#」を選択して
「New Template」のアイコンを押して
「Shortcut:」に summaryComment と入力して左のテキストエリアに

/// <summary>
/// $END$
/// </summary>

と入力して保存する

設定

    <s:Boolean x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/@KeyIndexDefined">True</s:Boolean>
    <s:Boolean x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Applicability/=Live/@EntryIndexedValue">True</s:Boolean>
    <s:Boolean x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Reformat/@EntryValue">True</s:Boolean>
    <s:Boolean x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Scope/=C3001E7C0DA78E4487072B7E050D86C5/@KeyIndexDefined">True</s:Boolean>
    <s:String x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Scope/=C3001E7C0DA78E4487072B7E050D86C5/CustomProperties/=minimumLanguageVersion/@EntryIndexedValue">2.0</s:String>
    <s:String x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Scope/=C3001E7C0DA78E4487072B7E050D86C5/Type/@EntryValue">InCSharpFile</s:String>
    <s:String x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Shortcut/@EntryValue">summaryComment</s:String>
    <s:Boolean x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/ShortenQualifiedReferences/@EntryValue">True</s:Boolean>
    <s:String x:Key="/Default/PatternsAndTemplates/LiveTemplates/Template/=7CE9083A8106EC40B5BD4EE5CFE79D50/Text/@EntryValue">/// &lt;summary&gt;
/// $END$
/// &lt;/summary&gt;</s:String>