Update following code review (#6)

Author: bendbennett

.changelog/6.txt

@@ -0,0 +1,3 @@
+```release-note:feature
+Added `SizeAtLeast()`, `SizeAtMost()` and `SizeBetween` validation functions to `mapvalidator` package
+```

mapvalidator/size_at_least.go

@@ -44,6 +44,13 @@ func (v sizeAtLeastValidator) Validate(ctx context.Context, req tfsdk.ValidateAt
 	}
 }
 
+// SizeAtLeast returns an AttributeValidator which ensures that any configured
+// attribute value:
+//
+//     - Is a Map.
+//     - Contains at least min elements.
+//
+// Null (unconfigured) and unknown (known after apply) values are skipped.
 func SizeAtLeast(min int) tfsdk.AttributeValidator {
 	return sizeAtLeastValidator{
 		min: min,

mapvalidator/size_at_most.go

@@ -44,6 +44,13 @@ func (v sizeAtMostValidator) Validate(ctx context.Context, req tfsdk.ValidateAtt
 	}
 }
 
+// SizeAtMost returns an AttributeValidator which ensures that any configured
+// attribute value:
+//
+//     - Is a Map.
+//     - Contains at most max elements.
+//
+// Null (unconfigured) and unknown (known after apply) values are skipped.
 func SizeAtMost(max int) tfsdk.AttributeValidator {
 	return sizeAtMostValidator{
 		max: max,

mapvalidator/size_between.go

@@ -46,6 +46,13 @@ func (v sizeBetweenValidator) Validate(ctx context.Context, req tfsdk.ValidateAt
 	}
 }
 
+// SizeBetween returns an AttributeValidator which ensures that any configured
+// attribute value:
+//
+//     - Is a Map.
+//     - Contains at least min elements and at most max elements.
+//
+// Null (unconfigured) and unknown (known after apply) values are skipped.
 func SizeBetween(min, max int) tfsdk.AttributeValidator {
 	return sizeBetweenValidator{
 		min: min,