git config --global diff.tool "meld"
git config --global difftool.prompt false
git config --global difftool.meld.path "C:\Program Files (x86)\Meld\Meld.exe"

.gitconfig

C:\Users\Username\.gitconfig

[diff]
	tool = meld
[difftool]
	prompt = false
[difftool "meld"]
	path = C:\\Program Files (x86)\\Meld\\Meld.exe