Any different guidance for tempdb with Availability Groups? I have an Availability Group set up on SQL Server 2014 running on a two-node Windows Server Failover Cluster. The setup consists of two stand-alone instances + synchronous with automatic failover.

Many Microsoft articles I've read advocate using multiple files for TempDB to increase performance. It seems they recommend using 8 files.

Should I do that in the case of a this configuration? Will it improve performance?
You pretty much always want more than a single TempDB file.  I'd certainly not go above 8 files in most situations; and probably more like 4.  Having said that, the only way to know the best configuration is to test it.

This applies equally to SQL Server instances of all kinds, including high availability setups, not just AlwaysOn Availability Groups.