[10.x] Document form.processing (#8834)

* Add processing docs

* Update precognition.md

* Update precognition.md

---------

Co-authored-by: Taylor Otwell <[email protected]>

Author: timacdonald

precognition.md

@@ -83,7 +83,9 @@ const submit = () => form.submit();
             {{ form.errors.email }}
         </div>
 
-        <button>Create User</button>
+        <button :disabled="form.processing">
+            Create User
+        </button>
     </form>
 </template>
 ```
@@ -161,6 +163,14 @@ const submit = () => form.submit()
     });
 ```
 
+You may determine if a form submission request is in-flight by inspecting the form's `processing` property:
+
+```html
+<button :disabled="form.processing">
+    Submit
+</button>
+```
+
 <a name="using-vue-and-inertia"></a>
 ### Using Vue & Inertia
 
@@ -254,7 +264,9 @@ export default function Form() {
             />
             {form.invalid('email') && <div>{form.errors.email}</div>}
 
-            <button>Create User</button>
+            <button disabled={form.processing}>
+                Create User
+            </button>
         </form>
     );
 };
@@ -327,6 +339,14 @@ const submit = (e) => {
 };
 ```
 
+You may determine if a form submission request is in-flight by inspecting the form's `processing` property:
+
+```html
+<button disabled={form.processing}>
+    Submit
+</button>
+```
+
 <a name="using-react-and-inertia"></a>
 ### Using React & Inertia
 
@@ -429,7 +449,9 @@ To enable live validation, you should bind the form's data to it's relevant inpu
         <div x-text="form.errors.email"></div>
     </template>
 
-    <button>Create User</button>
+    <button :disabled="form.processing">
+        Create User
+    </button>
 </form>
 ```
 
@@ -478,6 +500,14 @@ You may also determine if an input has passed or failed validation by passing th
 > **Warning**
 > A form input will only appear as valid or invalid once it has changed and a validation response has been received.
 
+You may determine if a form submission request is in-flight by inspecting the form's `processing` property:
+
+```html
+<button :disabled="form.processing">
+    Submit
+</button>
+```
+
 <a name="repopulating-old-form-data"></a>
 #### Repopulating Old Form Data