The answer is
.gitkeep isn’t documented, because it’s not a feature of Git.
Git cannot add a completely empty directory. People who want to track empty directories in Git have created the convention of putting files called .gitkeep in these directories. The file could be called anything; Git assigns no special significance to this name.
There is a competing convention of adding a .gitignore file to the empty directories to get them tracked, but some people see this as confusing since the goal is to keep the empty directories, not ignore them; .gitignore is also used to list files that should be ignored by Git when looking for untracked files.
This is not an answer to the original question "What are the differences between .gitignore and .gitkeep?" but posting here to help people to keep track of empty dir in a simple fashion. To track empty directory and knowling that .gitkeep is not official part of git,
just add a empty (with no content) .gitignore file in it.
So for e.g. if you have /project/content/posts and sometimes posts directory might be empty then create empty file /project/content/posts/.gitignore with no content to track that directory and its future files in git.
.gitkeep is just a placeholder. A dummy file, so Git will not forget about the directory, since Git tracks only files.
If you want an empty directory and make sure it stays 'clean' for Git, create a .gitignore containing the following lines within:
# .gitignore sample
###################
# Ignore all files in this dir...
*
# ... except for this one.
!.gitignore
If you desire to have only one type of files being visible to Git, here is an example how to filter everything out, except .gitignore and all .txt files:
# .gitignore to keep just .txt files
###################################
# Filter everything...
*
# ... except the .gitignore...
!.gitignore
# ... and all text files.
!*.txt
('#' indicates comments.)
.gitignore
is a text file comprising a list of files in your directory that git will ignore or not add/update in the repository.
.gitkeep
Since Git removes or doesn't add empty directories to a repository, .gitkeep is sort of a hack (I don't think it's officially named as a part of Git) to keep empty directories in the repository.
Just do a touch /path/to/emptydirectory/.gitkeep to add the file, and Git will now be able to maintain this directory in the repository.
Many people prefer to use just .keep since the convention has nothing to do with git.
Source: Stackoverflow.com