docs: clarify readonly

Author: dxinteractive

README.md

@@ -141,7 +141,7 @@ npm install --save dendriform
 - [Rendering](#rendering)
 - [Rendering arrays](#rendering-arrays)
 - [Setting data](#setting-data)
-- [Readonly forms](#readonly-forms)
+- [Read-only forms](#readonly-forms)
 - [Updating from props](#updating-from-props)
 - [ES6 classes](#es6-classes)
 - [ES6 maps](#es6-maps)
@@ -580,9 +580,9 @@ form.done();
 // form.value will update to become 3
 ```
 
-### Readonly forms
+### Read-only forms
 
-You may want to allow subscribers to a form, while also preventing them from making any changes. For this use case, the `readonly()` method returns a version of the form that cannot be set and cannot navigate history. Any forms branched off a readonly form will also be unable to set or navigate history.
+You may want to allow subscribers to a form, while also preventing them from making any changes. For this use case the `readonly()` method returns a version of the form that cannot be set and cannot navigate history. Calls to `set()`, `setParent()`, `undo()`, `redo()` and `go()` will throw an error. Any forms branched off a readonly form will also be read-only.
 
 ```js
 const form = new Dendriform(0);

packages/dendriform/README.md

@@ -141,7 +141,7 @@ npm install --save dendriform
 - [Rendering](#rendering)
 - [Rendering arrays](#rendering-arrays)
 - [Setting data](#setting-data)
-- [Readonly forms](#readonly-forms)
+- [Read-only forms](#readonly-forms)
 - [Updating from props](#updating-from-props)
 - [ES6 classes](#es6-classes)
 - [ES6 maps](#es6-maps)
@@ -580,9 +580,9 @@ form.done();
 // form.value will update to become 3
 ```
 
-### Readonly forms
+### Read-only forms
 
-You may want to allow subscribers to a form, while also preventing them from making any changes. For this use case, the `readonly()` method returns a version of the form that cannot be set and cannot navigate history. Any forms branched off a readonly form will also be unable to set or navigate history.
+You may want to allow subscribers to a form, while also preventing them from making any changes. For this use case the `readonly()` method returns a version of the form that cannot be set and cannot navigate history. Calls to `set()`, `setParent()`, `undo()`, `redo()` and `go()` will throw an error. Any forms branched off a readonly form will also be read-only.
 
 ```js
 const form = new Dendriform(0);