add-test-db.sh not executable on fresh clone

[Syedowais312]

Hi, @pashagolub @0xgouda

I noticed that docker/scripts/add-test-db.sh is referenced in README
as directly executable:

docker/scripts/add-test-db.sh

However, the file is committed with mode 100644 (non-executable),
which results in "permission denied" on fresh clones.

git ls-files --stage docker/scripts/add-test-db.sh shows:
100644 ...

Would you like me to open a PR to change the file mode to 100755?