fix refusing to merge unrelated histories code example

Example 1: fatal: refusing to merge unrelated histories

git pull origin master --allow-unrelated-histories

Example 2: fatal: refusing to merge unrelated histories

git pull --allow-unrelated-histories

Example 3: fatal: refusing to merge unrelated histories

git pull origin master --allow-unrelated-histories

Example 4: fatal: refusing to merge unrelated histories

git pull origin branchname --allow-unrelated-histories