Update ddpm.mdx (#2929)

docs/source/en/api/schedulers/ddpm.mdx

@@ -10,7 +10,7 @@ an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express o
 specific language governing permissions and limitations under the License.
 -->
 
-# Denoising diffusion probabilistic models (DDPM)
+# Denoising Diffusion Probabilistic Models (DDPM)
 
 ## Overview
 
@@ -24,4 +24,4 @@ We present high quality image synthesis results using diffusion probabilistic mo
 The original paper can be found [here](https://arxiv.org/abs/2010.02502).
 
 ## DDPMScheduler
-[[autodoc]] DDPMScheduler
\ No newline at end of file
+[[autodoc]] DDPMScheduler