Add comparison to `pangloss/vim-javascript` to Readme

[darcyparker]

https://github.com/othree/yajs.vim#differences-from-jeleravim-javascript-syntax compares yajs.vim to jelera/vim-javascript-syntax. I use pangloss/vim-javascript and in my observations, it is more popular than jelera/vim-javascript-syntax. (Compare stars).

I just learned about yajs and would like to see it compared to pangloss/vim-javascript.

[vyorkin]

It would be great if someone could add a few comments based on their own experience.

[jacks0n]

I was wondering the same thing myself, and did a quick comparison with ES6 and JSX files. Functionality and performance wise, I couldn't tell any difference. The colours were very different (same theme), it appears the plugins use different highlight groups:

Some examples:

JS Item	pangloss/vim-javascript	othree/yajs.vim
object key	jsObjectKey	javascriptObjectLabel
object curly bracket	jsObjectBraces	javascriptBraces
window	jsGlobalObjects	javascriptBOMWindowProp
Doc param name	jsDocParam	javascriptDocParamName
'const' keyword	jsStorageClass	javascriptVariable
window.oopen	jsFuncCall	javascriptDOMDocMethod