Manually document System.IO.BinaryWriter, StreamWriter, StringWriter, TextWriter (#2774)

* Manually document System.IO.StreamWriter and TextWriter

* Added BinaryWriter and StringWriter documentation

* suggestions by rpetrusha

Co-Authored-By: Ron Petrusha <[email protected]>

Author: carlossanlop

xml/System.IO/BinaryWriter.xml

@@ -546,8 +546,8 @@
       </ReturnValue>
       <Parameters />
       <Docs>
-        <summary>To be added.</summary>
-        <returns>To be added.</returns>
+        <summary>Asynchronously releases all resources used by the current instance of the <see cref="T:System.IO.BinaryWriter" /> class.</summary>
+        <returns>A task that represents the asynchronous dispose operation.</returns>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1543,8 +1543,8 @@
         <Parameter Name="buffer" Type="System.ReadOnlySpan&lt;System.Byte&gt;" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="buffer">To be added.</param>
-        <summary>To be added.</summary>
+        <param name="buffer">The span of bytes to write.</param>
+        <summary>Writes a span of bytes to the current stream.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>
@@ -1577,8 +1577,8 @@
         <Parameter Name="chars" Type="System.ReadOnlySpan&lt;System.Char&gt;" Index="0" FrameworkAlternate="netcore-2.1;netcore-2.2;netcore-3.0;netstandard-2.1" />
       </Parameters>
       <Docs>
-        <param name="chars">To be added.</param>
-        <summary>To be added.</summary>
+        <param name="chars">A span of chars to write.</param>
+        <summary>Writes a span of characters to the current stream, and advances the current position of the stream in accordance with the <see langword="Encoding" /> used and perhaps the specific characters being written to the stream.</summary>
         <remarks>To be added.</remarks>
       </Docs>
     </Member>