uses Bash's backtick for multiline bash with comment

Author: jmorat

doc/tutorial.adoc

@@ -180,7 +180,7 @@ kapture_pipeline_mapping.py -v info \
     -gfeat ./global_features/AP-GeM-LM18/global_features \
     -matches ./local_features/r2d2_500/NN_no_gv/matches \
     -matches-gv ./local_features/r2d2_500/NN_colmap_gv/matches \
-    --colmap-map ./colmap-sfm/r2d2_500/AP-GeM-LM18_top5  # lfeat type / map pairs \
+    --colmap-map ./colmap-sfm/r2d2_500/AP-GeM-LM18_top5  `# lfeat type / map pairs` \
     --topk 5
 ----