Updated readme

+ Tagged fianl build of v1.1 as Final1.1
+ Instruction to access last build of v1.1
+ Added instructions for arch file upgrade

README.md

@@ -63,6 +63,32 @@ docker pull ghcr.io/lnis-uofu/openfpga-master:latest
 docker run -it ghcr.io/lnis-uofu/openfpga-master:latest openfpga/openfpga bash
 ```
 
+## Backward compatibility with OpenFPGA v1.1
+
+OpenFPGA v1.2 is a major upgrade over v1.1, which upgrades the internal VPR engine.
+The (VPR) architecture files used with v1.1 may not be compatible with v1.2.
+
+You can upgrade your architecture files with script
+
+```bash
+python3 openfpga_flow/scripts/arch_file_updater.py \
+    --input_file ${v1.1_arch_file} \
+    --output_file ${v1.2_compatible_arch_file}
+```
+
+Or, If you want to stay with v1.1, the final build was (tag: [_OpenFPGA:Final1.1_](https://github.com/lnis-uofu/OpenFPGA/tree/Final1.1
+))
+
+```bash
+https://github.com/lnis-uofu/OpenFPGA/tree/Final1.1
+```
+
+or you can download the docker image
+
+```bash
+docker pull ghcr.io/lnis-uofu/openfpga-master:Final1.1
+```
+
 ## Documentation
 
 OpenFPGA's [full documentation](https://openfpga.readthedocs.io/en/master/) includes tutorials, descriptions of the design flow, and tool options.