message: Clarify status of soundness proof
diff: @@ -6,6 +6,7 @@ A formalization of the semantics for type checking and normalizing Pikelet.
  - [Introduction](#introduction)
  - [Notation](#notation)
  + - [Where is the soundness proof?](#where-is-the-soundness-proof)
  - [Syntax](#syntax)
  - [Raw terms](#raw-terms)
  - [Terms](#terms)
  @@ -31,6 +32,19 @@ universe hierarchy.
  TODO: describe BNF syntax and natural deduction here
  +### Where is the soundness proof?
  +
  +Here we are only defining the rules of our language's type checking and
  +evaluation. Further work needs to be done to verify that our system actually
  +satisfies certain interesting [type soundness properties][type-soundness],
  +like progress, preservation, [strong normalization][normalization-property],
  +etc. If you would like to discuss this with us, please check out
  +[the relevant github issue][formalization-issue]!
  +
  +[type-soundness]: https://en.wikipedia.org/wiki/Type_safety
  +[normalization-property]: https://en.wikipedia.org/wiki/Normalization_property_(abstract_rewriting)
  +[formalization-issue]: https://github.com/brendanzab/pikelet/issues/39
  +
  ## Syntax
  ### Raw terms
  