docs(eslint-plugin): add docs for signal-state-no-arrays-at-root-level (

#4549)

projects/ngrx.io/content/guide/eslint-plugin/rules/signal-state-no-arrays-at-root-level.md

@@ -10,3 +10,31 @@ signalState should accept a record or dictionary as an input argument.
 
 <!-- Everything above this generated, do not edit -->
 <!-- MANUAL-DOC:START -->
+
+## Rule Details
+
+This rule ensure that a Signal State shouldn't accept an array type at the root level.
+
+Examples of **correct** code for this rule:
+
+```ts
+const store = withState({ foo: 'bar' });
+
+const store = withState({ arrayAsProperty: ['foo', 'bar'] })
+
+const initialState = {};
+const store = signalStore(withState(initialState));
+```
+
+Examples of **incorrect** code for this rule:
+
+```ts
+const store = withState([1, 2, 3]);
+
+const store = withState([{ foo: 'bar' }]);
+
+const store = withState<string[]>([]);
+
+const initialState = [];
+const store = withState(initialState);
+```