[README] Add DX SDK to REQUIREMENTS

[L0FKA]

REQUIREMENTS
xlive
**Direct X 9 SDK (https://www.microsoft.com/en-us/download/details.aspx?id=6812)

or link to ms search, ask to look for 2010 release (https://www.microsoft.com/en-us/search/Results.aspx?q=DirectX%20Software%20Development%20Kit&form=DLC)
also make sure you've got DXSDK_DIR in your Variables

as option provide additional mirror if you want.

[niveuseverto]

Thanks, Will check this out!

[L0FKA]

I just wanted to merge my changes with anyone else, I did some tweaks to FOMM long ago, gonna merge and pull request, hope you'll review&merge it :)

[niveuseverto]

Of course I will check them =)
Right now I'm planning complete rewrite of fomod installation routine, as there are many problems with them (some of them are really hard to fix)