docs/flows/f4pga: update yosys website URL

Signed-off-by: Unai Martinez-Corral <umartinezcorral@antmicro.com>

docs/flows/f4pga.rst

@@ -134,7 +134,7 @@ Technology mapping in F4PGA toolchain
 
 .. _Xilinx 7 Series FPGAs Clocking Resources User Guide: https://www.xilinx.com/support/documentation/user_guides/ug472_7Series_Clocking.pdf#page=38
 .. _VTR FPGA Architecture Description: https://docs.verilogtorouting.org/en/latest/arch/
-.. _techmap section in the Yosys Manual: http://www.clifford.at/yosys/files/yosys_manual.pdf#page=153
+.. _techmap section in the Yosys Manual: http://yosyshq.net/yosys/files/yosys_manual.pdf#page=153
 
 It is important to understand the connection between the synthesis and
 implementation tools used in the F4PGA toolchain. As mentioned before,
@@ -405,8 +405,8 @@ More information
 ----------------
 
 Additional information about Yosys can be found on the `Yosys Project Website
-<http://www.clifford.at/yosys/>`_ , or in `Yosys Manual
-<http://www.clifford.at/yosys/files/yosys_manual.pdf>`_. You can also compile
+<https://yosyshq.net/yosys/>`_ , or in `Yosys Manual
+<http://yosyshq.net/yosys/files/yosys_manual.pdf>`_. You can also compile
 one of the tests described in Getting Started section and watch the log file
 to understand which operations are performed by Yosys.