python: Add interactive.py for a REPL during PnR

Signed-off-by: David Shah <dave@ds0.me>

python/interactive.py

diff --git a/python/interactive.py b/python/interactive.py
new file mode 100644
index 0000000..c8c359f
--- /dev/null
+++ b/python/interactive.py
@@ -0,0 +1,6 @@
+# Pass this file to one of the Python script arguments (e.g. --pre-place interactive.py)
+# to drop to an command-line interactive Python session in the middle of place and route 
+
+import code
+print("Press Ctrl+D to finish interactive session")
+code.interact(local=locals())