The license requires you to reproduce the license notice, which consists of
- the copyright notice of the BSD-licensed software
- the BSD license itself, which consists of the list of conditions annd a disclaimer.
For binaries, the license requires you to include this notice in “the documentation and/or other materials provided with the distribution.” The intention seems to be that the notice can be seen by an ordinary user.
Nowadays, a lot of software does not have any materials provided with the distribution, e.g. mobile apps. Instead, the software itself contains relevant documentation. It is normal to provide the notice in human-readable form within the app, typically in a menu item like Settings → About → Open Source or Help → Legal Information.
If you provide documentation to the software but this documentation is not provided together with the binary, then I don't think a notice in the documentation would satisfy the license. For example, an online manual might be insufficient, especially since such documentation would be unavailable when the user doesn't have an active internet connection.