[doc] add coverage description in readme

readme.md

@@ -37,7 +37,7 @@ It's build script is in `nix/gcd` folder, providing the below attributes:
 * [{tb,formal}-]rtl: SystemVerilog generated from the lowered MLIR bytecode
 * tb-dpi-lib: DPI library written in Rust for both Verilator and VCS
 * verilated[-trace]: C++ simulation executable and libaray generated by Verilator with/without `fst` waveform trace
-* vcs[-trace]: C simulation executable compiled by VCS with/without `fsdb` waveform trace
+* vcs[-trace]: C simulation executable compiled by VCS with/without `fsdb` waveform trace and 'coverage.vdb' for coverage report
 * jg-fpv: Formal Property Verification report generated by JasperGold
 
 To get the corresponding output, developers can use:
@@ -90,6 +90,14 @@ nix run '.#gcd.vcs-trace' --impure -- +dump-start=0 +dump-end=10000 +wave-path=t
 
 The DPI lib can automatically match the arguments and does not interact with VCS. In this case, the first three parameters will be passed to the DPI lib to control waveform generation, and the last parameter will be passed to the VCS to dump the results of all sva statements.
 
+To generate the coverage report, you can run:
+
+```bash
+urg -dir gcd-sim-result/result/coverage.vdb/
+``
+
+The coverage report will be generated in the `./urgReport` directory.
+
 * Note that in order to use VCS for simulation, you need to set the environment variables `VC_STATIC_HOME` and `SNPSLMD_LICENSE_FILE` and add the`--impure` flag.
 
 To run the formal property verification. Then you can run: