With the release of SQL Server 2017, Reporting Services is now a separate installation. The installer can be downloaded from the Microsoft Download Center and installed in either a free edition (Evaluation, Express, or Developer) or a paid edition with a product key. It can also be installed silently, and in this blog post, I describe how. As a bonus, I also cover some basic configuration using the rsconfig command line utility.
The installer executable has several command line parameters, which you can view using the /? parameter:
Thus, a command line to silently install the Developer edition of Reporting Services would be this:
SQLServerReportingServices.exe /quiet /norestart /IAcceptLicenseTerms /Edition=Dev
After installation is complete, the Reporting Services instance (named SSRS) is unconfigured. The Report Server Configuration Manager GUI is available to configure it. If you need to continue automated and/or silently, the rsconfig tool is available. The command line below will configure Reporting Services to use the service accounts to connect to a (new) database ReportServer on the localhost default instance of SQL Server:
rsconfig -c -s localhost -d ReportServer -a Windows -i SSRS
Note: The -i parameter specifies the name of the Reporting Services instance, which is SSRS. Unlike the current docs state, it does not specify the instance name of SQL Server where you will host the report server database.
As a follow-up, I wrote a more complete guide on configuring the report server with PowerShell and WMI.
Sven Aelterman 
Just ran into an issue with the SSRS installer. The command line parameter Edition does not accept ‘ExprAdv’. The following was logged in the SSRS install log that gets saved in %TEMP%\SSRS:
e000: Error: Did not recogonize edition ExprAdv. Valid editions: EVAL, DEV, EXPR.