[Configs]: just a get this working configurations for user area example..

openlane/user_proj_example/config.tcl

diff --git a/openlane/user_proj_example/config.tcl b/openlane/user_proj_example/config.tcl
index 20eb097..ca6d3e9 100644
--- a/openlane/user_proj_example/config.tcl
+++ b/openlane/user_proj_example/config.tcl
@@ -6,6 +6,7 @@
 	$script_dir/../../verilog/rtl/defines.v \
 	$script_dir/../../verilog/rtl/user_proj_example.v"
 
+set ::env(CLOCK_PORT) ""
 set ::env(CLOCK_NET) "counter.clk"
 set ::env(CLOCK_PERIOD) "10"