Fix up ford deletion of gitignore

Author: znicholls

docs/gen_fortran_api.py

@@ -6,6 +6,9 @@
 
 import shutil
 import subprocess
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).parents[1]
 
 ford = shutil.which("ford")
 if ford is None:
@@ -16,3 +19,6 @@
     [ford, "ford_config.md"],
     check=True,
 )
+
+# Put back the gitkeep file which ford deletes
+(REPO_ROOT / "docs" / "fortran-api" / ".gitkeep").touch()