Fix README markdown

[Yukaii]

Changes

• add extra line after heading(MD022)
• trim trailing whitespace
• change tab(hard tab) in Structure section to white spaces, make it aligned beautiful again 😆
• add link for operational tranformation

[jackycute]

Thank you @Yukaii !
First seeing that markdownlint stuff, really helpful.

[jackycute]

I've also noticed other rules in the lint.
Will try to fit them into current editor behaviors.

[jackycute]

As you see, when you trim the trailing spaces for new line, it will break the layout on the GitHub.
HackMD use breaks while GitHub use 2 trailing spaces for break.
But the README.md here is more for GitHub, may consider add them back.
What do you think?

[Yukaii]

I haven't noticed yet, sorry about that.

In markdown, we might need an extra line to do correct line break 😓 , but there will be the larger line height on GitHub.

[jackycute]

So how about we add back the trailing spaces, it's necessary for GitHub.
The lint rules also mentioned that if you use two spaces for new line, it's allow to change that rule.

[Yukaii]

OK!