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

.gitconfig

C:\Users\Username\.gitconfig

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