[Doc] Add README for Modelsim workspace

MSIM/README.md

@@ -0,0 +1,12 @@
+# Skywater PDK
+This directory is the workspace for running Mentor Modelsim simulations for FPGA fabrics
+Please keep this directory clean and organize as follows:
+- Each task-run should be placed in a separated directory
+- **common**: include commonly used scripts for post-PnR verification 
+- READMD is the only file allowed in the directory, others should be sub-directories.
+
+* Quick Example to run simulations for task-run
+
+```
+python3 run_post_pnr_msim_task.py --testbench_dir_name ../../TESTBENCH/k4_N8_caravel_io_FPGA_12x12_fdhd_cc --task_name k4_N8_caravel_io_FPGA_12x12_fdhd_cc
+```