add WIRE_RC_LAYER to the common config.tcl

sky130/openlane/config.tcl

diff --git a/sky130/openlane/config.tcl b/sky130/openlane/config.tcl
index 757d298..a43b4eb 100755
--- a/sky130/openlane/config.tcl
+++ b/sky130/openlane/config.tcl
@@ -56,4 +56,7 @@
 set ::env(FP_PDN_CORE_RING_VSPACING) 5
 set ::env(FP_PDN_CORE_RING_HSPACING) 5
 set ::env(FP_PDN_CORE_RING_VOFFSET) 20
-set ::env(FP_PDN_CORE_RING_HOFFSET) 20
\ No newline at end of file
+set ::env(FP_PDN_CORE_RING_HOFFSET) 20
+
+# Used for estimate_parasitics
+set ::env(WIRE_RC_LAYER) "met1";