git vimdiff: set local file writeable

setup

@@ -12,7 +12,9 @@ if [[ $git_version == 1.9* ]]; then
     git config --global push.default simple
 fi
 
+# diff
 git config --global diff.tool vimdiff
+git config --global difftool.vimdiff.cmd 'vim -R -f -d -c "wincmd l" -c '\''cd "$GIT_PREFIX"'\'' -c "set noro" "$LOCAL" "$REMOTE"'
 
 # aliases
 git config --global alias.branches "branch --all"