Merge 2 repos together and preserve that sweet sweet commit history

merge_RepoB->RepoA

# Beware this will not create a subfolder for RepoB in RepoA

If you want to merge project-b into project-a:

cd path/to/project-a
git remote add project-a path/to/project-b
git fetch project-b --tags
git merge --allow-unrelated-histories project-b/master
git remote remove project-b