Add usage comments

Former-commit-id: 0555309a2862e24dbcfbce54f2b692de10c155f4
Former-commit-id: 168cc16706190b0067e1db06e912500284a8b24d
Former-commit-id: 1bb43330a521100642bfbab85f3c052941b297c7

src/ImageProcessorCore/Formats/Bmp/BmpEncoderCore.cs

@@ -42,6 +42,7 @@ namespace ImageProcessorCore.Formats
                 rowWidth += 4 - amount;
             }
 
+            // Do not use IDisposable pattern here as we want to preserve the stream. 
             EndianBinaryWriter writer = new EndianBinaryWriter(EndianBitConverter.Little, stream);
 
             int bpp = (int)this.bmpBitsPerPixel;

src/ImageProcessorCore/Formats/Gif/GifEncoderCore.cs

@@ -56,6 +56,7 @@ namespace ImageProcessorCore.Formats
                 this.Quantizer = new OctreeQuantizer { Threshold = this.Threshold };
             }
 
+            // Do not use IDisposable pattern here as we want to preserve the stream. 
             EndianBinaryWriter writer = new EndianBinaryWriter(EndianBitConverter.Little, stream);
 
             // Ensure that quality can be set but has a fallback.