The markdown of installation page partly doesn't work

[JiaxiangBU]

In the installation page, the markdown fails for the choice (Mac, R, CPU). Here is the screenshot.

[lanking520]

@JiaxiangBU thank you for letting us know. @aaronmarkham could you please check the reason for this? I got the same output as shown above.
@mxnet-label-bot please add [doc, R]

[aaronmarkham]

Looks like the Docker instructions broke the page as these Docker instructions are showing up in the Windows --> Python --> CPU --> Build from Source block. And build from source isn't appearing as expected. Snowball effect... as the R stuff comes after that Docker section.

There looks to be a variety of spots where things are not being encoded properly. Wish we could get rid of this selector.... but I'll see if I can fix it.