Make the README example run to the end

It needs zod, which this package does not depend on, so the import now
says to install it. assertFields threw on the drift the example shows on
purpose, which stopped the script before the coverage part; it is now a
commented alternative to the expectFields report.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -53,7 +53,7 @@ assessed. Reports use the `@extant2000/evidence-record` format.
 
 ```ts
 import { assertShape, expectFields, assertFields, formatFields, coverage, formatCoverage } from '@extant2000/contract-check'
-import { z } from 'zod'   // or any parser with a zod-style safeParse
+import { z } from 'zod'   // npm install zod, or use any parser with a zod-style safeParse
 
 // 1. Response shape
 const payload: unknown = { id: 'm1', name: 'Survey' }   // e.g. a parsed response body
@@ -68,7 +68,7 @@ const expectations = [
 ]
 const result = expectFields(subscription, expectations)
 console.log(formatFields(result, { context: 'stripe.subscriptions.create', expectations }))
-assertFields(subscription, expectations, 'stripe.subscriptions.create')   // or throw
+// assertFields(subscription, expectations, 'stripe.subscriptions.create')   // throws ContractDriftError here instead
 
 // 3. Coverage against a floor
 const c = coverage(['GET /a', 'GET /b', 'POST /c', 'GET /d'], ['GET /a', 'GET /b', 'POST /c'], 80)