[tools/mec] Update README.md (#14357)

It adds a simple guide to HOWTO page for who wants to build and
test the circle adapter.

ONE-DCO-1.0-Signed-off-by: Jonghwa Lee <[email protected]>

tools/model_explorer_circle/HOWTO.md

@@ -1,3 +1,26 @@
+## How to test
+* Prerequisites
+```
+python -m venv venv
+source ./venv/bin/activate
+```
+
+* Install module to virtual environment (Editable mode)
+```
+pip install -e .
+```
+
+* Execute Model Explorer with Circle adapter extension
+```
+model-explorer --extensions circle_adapter --no_open_in_browser
+```
+
+* Execute Unittest
+```
+pip install pytest
+pytest
+```
+
 ## How to generate Circle schema python script
 
 (This is not mandatory since it already included default Circle schema generated by following procedure.)