[Bug][Blog Submission] Blog submission process needs to be improved

### Search before asking

- [X] I had searched in the [issues](https://github.com/apache/incubator-devlake-website/issues?q=is%3Aissue) and found no similar issues.

### What happened

The current [blog submission doc](https://devlake.apache.org/community/MakingContributions/BlogSubmission/) has only 5 steps mentioned but there is more to it.


### What do you expect to happen

Here are additional steps that needs to be added in blog submission doc:
1. Add your details in `info/Blog/AllPosts.json`
2. Upload the cover image that will be shown in [Blog Overview page](https://devlake.apache.org/blogOverview) in `static/img/Blog` folder

### Anything else

_No response_

### Version

main

### Are you willing to submit PR?

- [X] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://www.apache.org/foundation/policies/conduct)