test: add .env.example file with its description to integration-tests Readme.md #221

All 1 807 tests pass, 1 skipped in 3m 12s

      3 files ±0   237 suites ±0 3m 12s ⏱️ - 1m 3s
1 808 tests ±0 1 807 ✔️ ±0 1 💤 ±0 0 ❌ ±0
1 833 runs ±0 1 832 ✔️ ±0 1 💤 ±0 0 ❌ ±0

Results for commit deb9667. ± Comparison against earlier commit 8ac53d9.