git log command has a bunch of flags that you can use to filter
commits and format their output.
We can get
git log to only show the date for a commit in the
format with the following flags:
$ git log --pretty=format:"%ad" --date=short
We can also get
git log to filter commits to just those that have files
$ git log --diff-filter=A
git commands, we can restrict the output to those that match a
path or file.
$ git log -- README.md
If we put all of these together, then we have a one-line command for getting the date a specific file was added to the repository:
$ git log --pretty=format:"%ad" --date=short --diff-filter=A -- README.md 2015-02-06
man git-log for more details.