Fill in some missing docs for SqlClient (#3417)

* Fill in some missing docs for SqlClient

* Fix build error

Author: roji

xml/System.Data.SqlClient/SqlDataReader.xml

@@ -246,9 +246,17 @@
         <Parameter Name="disposing" Type="System.Boolean" Index="0" FrameworkAlternate="netcore-2.0;netcore-2.1;netcore-2.2;netcore-3.0" />
       </Parameters>
       <Docs>
-        <param name="disposing">To be added.</param>
-        <summary>To be added.</summary>
-        <remarks>To be added.</remarks>
+        <param name="disposing">
+          <see langword="true" /> to release managed and unmanaged resources; <see langword="false" /> to release only unmanaged resources.</param>
+        <summary>Releases the managed resources used by the <see cref="T:System.Data.SqlClient.SqlDataReader" /> and optionally releases the unmanaged resources.</summary>
+        <remarks>
+          <format type="text/markdown"><![CDATA[
+
+## Remarks
+ This method calls <xref:System.Data.SqlClient.SqlDataReader.Close%2A>.
+
+]]></format>
+        </remarks>
       </Docs>
     </Member>
     <Member MemberName="FieldCount">
@@ -656,8 +664,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Gets the column schema (<see cref="T:System.Data.Common.DbColumn" /> collection).</summary>
+        <returns>The column schema (<see cref="T:System.Data.Common.DbColumn" /> collection).</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>