Update postStart.sh

Author: vgvoleg

.devcontainer/commands/postStart.sh

@@ -4,5 +4,8 @@ set -e
 
 # Install dependencies
 pip install -r requirements.txt
-# Install test dependencies
-# pip install -r test-requirements.txt
+# Install ydb package
+pip install -e .
+# Install tox for CI
+pip install tox
+