Update read options

Signed-off-by: Rafal Kapuscik <rkapuscik@antmicro.com>

systemverilog-plugin/uhdmcommonfrontend.cc

diff --git a/systemverilog-plugin/uhdmcommonfrontend.cc b/systemverilog-plugin/uhdmcommonfrontend.cc
index cdf710e..7fd3871 100644
--- a/systemverilog-plugin/uhdmcommonfrontend.cc
+++ b/systemverilog-plugin/uhdmcommonfrontend.cc
@@ -65,13 +65,19 @@
     log("        parameters of modules yield invalid or not synthesizable code.\n");
     log("        Needs to be followed by read_systemverilog -link after reading\n");
     log("        all files.\n");
+    log("\n");
     log("    -link\n");
     log("        performs linking and elaboration of the files read with -defer\n");
+    log("\n");
     log("    -parse-only\n");
     log("        this parameter only applies to read_systemverilog command,\n");
     log("        it runs only Surelog to parse design, but doesn't load generated\n");
     log("        tree into Yosys.\n");
     log("\n");
+    log("    -formal\n");
+    log("        enable support for SystemVerilog assertions and some Yosys extensions\n");
+    log("        replace the implicit -D SYNTHESIS with -D FORMAL\n");
+    log("\n");
 }
 
 void UhdmCommonFrontend::execute(std::istream *&f, std::string filename, std::vector<std::string> args, RTLIL::Design *design)