Sometimes, you want to exclude all the (for instance) .class or .jar files
from git. In that case, you would create a .gitignore folder at the top of
your repository with contains like this:
*.class
*.jar
On the other hand, sometimes you also want to include certain .class or .jar
files in only several directories. In that case, you would create a .gitignore
in those particular directories like this:
!*.class
!*.jar
The key symbol here is the ! symbol.
Git operates by reading the repository-level .gitignore but will override any
settings upon reading a directory-level .gitignore.