ICU-20087 [WIP] Convert HTML readme files to Markdown

[revolter]

Checklist

• Issue filed: https://unicode-org.atlassian.net/browse/ICU-20087
• Updated PR title and link in previous line to include Issue number
• Issue accepted
• Tests included
• Documentation is changed or added

@srl295, Is this the way to go?

Preview: https://github.com/unicode-org/icu/blob/1b4ff472ff323874654eb363e3289b88d0f3d298/icu4c/README.md

[srl295]

@revolter sorry for the late response.

Yes, I really like this! 👍 thank you.

I think some of the content may want to split off into a wiki, or BUILDING.md or whatever eventually. But, it is surely to end up in Markdown format, so this is useful work. (If the complex tables such as "source code organization" are easier to import as an HTML chunk, please feel free to do that for now.)

Thanks. There may be commit 9a5b7af since you did the conversion, we'll want to compare the readme.html with master to make sure nothing was lost.

[revolter]

The bad thing is that this is very time-consuming, but I'll see what I can do.

[markusicu]

In the meantime, we did move our readme files into Markdown.