Add an example for arbitrary type validation upon deserialization. #148
  Add this suggestion to a batch that can be applied as a single commit.
  This suggestion is invalid because no changes were made to the code.
  Suggestions cannot be applied while the pull request is closed.
  Suggestions cannot be applied while viewing a subset of changes.
  Only one suggestion per line can be applied in a batch.
  Add this suggestion to a batch that can be applied as a single commit.
  Applying suggestions on deleted lines is not supported.
  You must change the existing code in this line in order to create a valid suggestion.
  Outdated suggestions cannot be applied.
  This suggestion has been applied or marked resolved.
  Suggestions cannot be applied from pending reviews.
  Suggestions cannot be applied on multi-line comments.
  Suggestions cannot be applied while the pull request is queued to merge.
  Suggestion cannot be applied right now. Please check back later.
  
    
  
    
This adds an example for a useful pattern where a type needs to be validated arbitrarily (via
TryFromon an inner type) during deserialization. This comes directly from serde-rs/serde#642 (comment) where I learned the pattern.I couldn't figure out on my own how to do this via browsing https://serde.rs, so I went to the issue tracker where I found this recipe, so it seems like a good candidate for the examples section.