Fix typo in title and better narrative (#15902)

A better narrative for #15004, and fix typo in title

Signed-off-by: Harry Zhang <lei.zhang@alibaba-inc.com>

README.md

@@ -100,6 +100,6 @@ To provide that support the API versions of objects should be those that work fo
 
 This project is still under active development, so you might run into [issues](https://github.com/helm/charts/issues). If you do, please don't be shy about letting us know, or better yet, contribute a fix or feature.
 
-## Happy helming in China
+## Happy Helming in China
 
-If you are in China, there are some problems to use Helm Charts directly (e.g. gcr.io, googleapis.com etc), you can use this mirror repo at https://github.com/cloudnativeapp/charts.
+If you are in China, there are some problems to use upstream Helm Charts directly (e.g. images hosted on `gcr.io`, `quay.io`, and Charts hosted on `googleapis.com` etc), you can use this mirror repo at https://github.com/cloudnativeapp/charts which automatically sync & replace unavailable image & repo URLs in every Chart.