Provide explicit ref to Value Completion section (graphql#982)

Co-authored-by: Benjie Gillam <benjie@jemjie.com>
Co-authored-by: Roman Ivantsov <roman.ivantsov@microsoft.com>

Author: 3 people

spec/Section 3 -- Type System.md

@@ -856,7 +856,7 @@ Produces the ordered result:
 **Result Coercion**
 
 Determining the result of coercing an object is the heart of the GraphQL
-executor, so this is covered in that section of the spec.
+executor, see [Value Completion](#sec-Value-Completion).
 
 **Input Coercion**