Merge pull request #37 from joshorr/josho/better-mypy-support-and-auto-off-by-default

docs: add info about how `Missing` is always `False`-like, etc.

Author: joshorr

README.md

@@ -8,6 +8,7 @@
         + [Explicitly Defined Partials - Basic Example](#explicitly-defined-partials---basic-example)
         + [Automatically Defined Partials - Basic Example](#automatically-defined-partials---basic-example)
     * [More Details](#more-details)
+        + [Missing](#missing)
         + [Inheritable](#inheritable)
         + [Exclude Fields from Automatic Partials (AutoPartialModel)](#exclude-fields-from-automatic-partials-autopartialmodel)
         + [Auto Partials Configuration](#auto-partials-configuration)
@@ -159,6 +160,13 @@ This includes any inherited Pydantic fields (from a superclass).
 
 ## More Details
 
+### Missing
+
+The `Missing` value is a sentinel, and there is never more than one instance of it. So you can use the `is` operator with it,
+just like you would with `None`.  It's of type `MissingType`.
+
+When evaluated as a bool, `Missing` is always `False`; just like how `None` evaluates to `False`.
+
 ### Inheritable
 
 With `AutoPartialModel`, you can inherit from a model to make an automatic partial-version of the inherited fields: