Mention ExifTool for reading and writing metadata

Author: uschille

episodes/02-image-basics.md

@@ -1037,7 +1037,13 @@ Metadata holds information about the image itself,
 such as when the image was captured,
 where it was captured,
 what type of camera was used and with what settings, etc.
-We normally don't see this metadata when we view an image,
+Many popular image editing programs have built-in metadata viewing
+capabilities. A platform-independent open-source tool that allows
+users to read, write, and edit metadata is
+[ExifTool](https://exiftool.org/). It can handle a wide range of file
+types and metadata formats but requires some technical knowledge to be
+used effectively.
+We normally don't see the metadata when we view an image using Python and imageio,
 but we can view it independently if we wish to
 (see [*Accessing Metadata*](#accessing-metadata), below).
 The important thing to be aware of at this stage is that