You may have seen badges in READMEs of different repos - maybe in Github, Gitlab or Bitbucket. You may have also wondered why people are embedding them in their repos and how could they be helpful to users. If so, this is the right place for you.
Others also welcome to read as this could contain some valuable stuff

There are many reasons people adding badges to their README.

• Because they are visaully appealing
• Because they provide information simply and sweetly and quickly

Usually repos with badges attract users more than projects without badges in their README. Badges are a good way to show your colours and the quality of your product. Also it gives a pleasant view to your users.

Most importantly, they can communicate the information of your project very quickly. People usually display their project's build status, coverage reports, documentation, social status quickly using the badges.

Here are the things that I found as the most essential badges to include in your repo.

Build status

This tells us about how the current project base performed in the CI pipelines and tests of different kinds - you may include many reasons as possible. Generally most of the CI providers give you a nice looking badge to include in your README. Here are some examples

It is better if you could insert the corresponding link for every badge you insert

Code coverage

Code coverage tells the performance of the tests created simply. It checks for lines and statements covered by statements to create the coverage reports. Many coverage report providers give you another badge to include in your repository (codecov and coveralls are 2 providers that I personally like)

Code quality

Code quality is another important thing to maintain a long-term project. It allows people not to mix styles and make a complete mess. It also helps to avoid mistakes we often do in programming.

License

A good way to catch the user's attention to license is creating a badge. There are many ways to include badges about license and I found shields.io as the easiest.

You can simply create the badge you want by filling the relevant details there.
https://shields.io/category/license

Social status

If you are looking for people to contribute your project more often, the best way is to keep social. Social status badges enforces your users to see the social status of you and your projects and will also help you to catch contributors to other projects as well. There are many categories under this. This may also include donation links. Following are the most important things for me. I'm using shields.io for this one as well.
Follow the link

• Github stars
• Github followers
• Github forks
• Twitter followers
• Open collective backers
• First timers only

There could be more and more reasons to add badges to your repo. Let me know if you found more.

PS: I'm using shields.io to make awesome badges. You may also try it
PS++: I'm new to blogging. So please let me know if I doing something wrong