Clarified installation step and fixed markdown lint issues

[phoityne]

Hi.

Thanks for your contribution. But, there are some old information included, because I'm just prepareing README HEAD for new version. It is planning that ships for ghc-8.8.

• In next version, we are using these 3 libs. ghci-dap, haskell-dap, haskell-debug-adapter
• No need to add --with-ghc option. It will be added by phoityne automatically. "--with-ghc=ghci-dap"

Actually, you can use these 3 libs wright now. Please see README HEAD and Quick Setup Video.

I will check markdown lint issues. Regards.

[freeman42x]

@phoityne Cool, I'll close the PR then.