[Docs] Add mmengine logo in docs (#641)

* [Docs] Add mmengine logo in docs

* Remove generated changelog.md

docs/en/_static/css/readthedocs.css

 table.colwidths-auto td {
   width: 50%
 }
+.header-logo {
+    background-image: url("../image/mmengine-logo.png");
+    background-size: 130px 40px;
+    height: 40px;
+    width: 130px;
+}

docs/zh_cn/_static/css/readthedocs.css

 table.colwidths-auto td {
   width: 50%
 }
+.header-logo {
+    background-image: url("../image/mmengine-logo.png");
+    background-size: 130px 40px;
+    height: 40px;
+    width: 130px;
+}