egui_wgpu, added disclaimer, discourages people calling render without update_buffer (#7971)

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* Closes <https://github.com/emilk/egui/issues/THE_RELEVANT_ISSUE>
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Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

crates/egui-wgpu/src/renderer.rs

@@ -470,6 +470,9 @@ impl Renderer {
     /// The render pass internally keeps all referenced resources alive as long as necessary.
     /// The only consequence of `forget_lifetime` is that any operation on the parent encoder will cause a runtime error
     /// instead of a compile time error.
+    ///
+    /// # Panic
+    /// Always ensure that [`Renderer::update_buffers`] has been called otherwise calling [`Renderer::render`] will panic!
     pub fn render(
         &self,
         render_pass: &mut wgpu::RenderPass<'static>,