How to doc - Adding dependency to stage

content/docs/sidebar.json

@@ -100,7 +100,7 @@
         "slug": "how-to",
         "source": false,
         "children": [
-          "add-output-to-stage",
+          "add-dependency-or-output-to-stage",
           "undo-adding-data",
           "update-tracked-files"
         ]

content/docs/user-guide/how-to/add-dependency-or-output-to-stage.md

@@ -0,0 +1,50 @@
+# Add Dependency or Output to Stage
+
+There are situations where we have executed a stage (either by writing
+`dvc.yaml` manually and using `dvc repro`, or with `dvc run`), but later notice
+that some of the dependencies, or the output files/directories it creates, which
+are already in the <abbr>workspace</abbr>, are missing from `dvc.yaml` (`deps`
+and `outs` field respectively). Follow the steps below to add existing files or
+directories as <abbr>dependency</abbr> or <abbr>outputs</abbr> to a stage
+without re-executing it again, which can be expensive/time-consuming, and is
+unnecessary.
+
+We start with an example `prepare`, which has a single dependency and output. To
+add a missing dependency `data/data.csv` and output `data/validate` to this
+stage, we can edit `dvc.yaml` like this:
+
+```git
+ stages:
+   prepare:
+     cmd: python src/prepare.py
+     deps:
++    - data/data.csv
+     - src/prepare.py
+     outs:
+     - data/train
++    - data/validate
+```
+
+> Note that you can also use `dvc run` with the `-f` and `--no-exec` options to
+> add another dependency/output to the stage:
+>
+> ```dvc
+> $ dvc run -f --no-exec \
+>           -n prepare \
+>           -d data/data.csv \
+>           -d src/prepare.py \
+>           -o data/train \
+>           -o data/validate \
+>           python src/prepare.py
+> ```
+>
+> `-f` overwrites the stage in `dvc.yaml`, while `--no-exec` updates the stage
+> without executing it.
+
+Finally, we need to run `dvc commit` to save the newly specified dependency or
+output(s) to the <abbr>cache</abbr> (and to update the corresponding hash values
+in `dvc.lock`):
+
+```dvc
+$ dvc commit
+```