docs: correct wording of heading

Jamie Tanna · jamietanna · commit b7b82be741ef · 2024-09-20T21:26:12.000+01:00
diff --git a/README.md b/README.md
@@ -1893,7 +1893,7 @@ components:
 
 So how do we get `oapi-codegen` to generate our code?
 
-### Using a single package, with multiple OpenAPI spec for a given package
+### Using a single package with multiple OpenAPI specs
 
 <a name=import-mapping-self></a>
 
