Update wiki for merging multiple repositories in Windows

[bh3605]

The wiki article to merge multiple repositories is only for UNIX based systems.

Here's how you handle this in Windows.

gource --output-custom-log repo1.txt "repo1/filepath"
gource --output-custom-log repo2.txt "repo2/filepath"
type repo1.txt repo2.txt > combined.txt
sort combined.txt > sortedcombined.txt