feat: bring in TAMU ACTVISg200 and ACTVISg500

electric-grid/physical/synthetic/ACTIVSg200/README.md

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+# Overview
+
+## Illinois 200-Bus System: ACTVISg200
+
+The ACTIVSg200 case is a 200 bus power system test case that is entirely synthetic, built from public information and a statistical analysis of real power systems. It bears no relation to the actual grid in this location, except that generation and load profiles are similar.
+
+The case is provided in PowerWorld format, Matpower format, PSS/E raw format, and PSLF epc format, along with the corresponding files for the transient stability models.
+
+## Model Image
+
+![Model Image](assets/figIL200.jpg)
+![Model Image](assets/Illinois200.png)
+
+## References
+
+[Source](https://electricgrids.engr.tamu.edu/electric-grid-test-cases/activsg200/)

electric-grid/physical/synthetic/ACTIVSg500/README.md

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+# Overview
+
+## SouthCarolina 500-Bus System: ACTVISg500
+
+The ACTIVSg500 case is a 500 bus power system test case that is entirely synthetic, built from public information and a statistical analysis of real power systems. It bears no relation to the actual grid in this location, except that generation and load profiles are similar.
+
+The case is provided in PowerWorld format, Matpower format, PSS/E raw format, and PSLF epc format.
+
+## Model Image
+
+![Model Image](assets/figSC500.jpg)
+![Model Image](assets/SouthCarolina500.png)
+
+## References
+
+[Source](https://electricgrids.engr.tamu.edu/electric-grid-test-cases/activsg500/)