There are two ways to do this. You can add details globally so that these details are added to every report automatically, or you can add these on a per-project/report basis. A company logo can only be added through Settings.
1) From any page, move your mouse over the Menu button in the top right corner.
2) Click on "Settings".
3) On the next page, navigate to the "Company Settings" section.
4) You will see options for Auditor Company and Auditor Name, as well as the Company Logo option.
Manual (Per-report basis)
1) Access the Project you wish to edit.
2) From the Project Summary page, click on "Add Signature" (this will read "Edit Signature" if a signature is already added).
3) You will see a section for Auditor Company and Auditor Name here. Details entered here will only be used for this particular project.