Github doesn't detect new folder
Git will ignore empty folders. Make sure at least one file is present in the new folder in the Git repository, or else you are not able to add it.
If your directory structure looks like this:
/------WebsiteName/
|
|-----------/Mobile/
Then make sure you are in WebsiteName directory, then run git status
If you are still getting the same error then run the following in order:
git init
git status //here you should see the mobile folder and its files
git add --all
git commit -am "committing"
git push --all
In that case you should check whether you have put /mobile
in your .gitignore file. Or the solution provided by @meda would work.