add more useful msg to nbdev_export

Author: hamelsmu

nbs/api/05_doclinks.ipynb

@@ -364,8 +364,8 @@
     "    if os.environ.get('IN_TEST',0): return\n",
     "    if not is_nbdev(): raise Exception('`nbdev_export` must be called from a directory within a nbdev project.')\n",
     "    if procs:\n",
-    "      import nbdev.export\n",
-    "      procs = [getattr(nbdev.export, p) for p in L(procs)]\n",
+    "        import nbdev.export\n",
+    "        procs = [getattr(nbdev.export, p) for p in L(procs)]\n",
     "    files = nbglob(path=path, as_path=True, **kwargs).sorted('name')\n",
     "    for f in files: nb_export(f, procs=procs)\n",
     "    add_init(get_config().lib_path)\n",