Add README files for pipelines directories.

pipelines/README.md

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+# Pipeline Definitions
+
+This directory contains pipeline definition YAML files which are used
+to verify calibration products with the LSST Science Pipelines.
+The pipelines defined here are science ready and come in two flavors:
+generic ("ingredients") and camera-specific (within appropriately
+named sub-directories).  Use of camera-specific pipelines is strongly
+encouraged where possible as they are optimized for the particular
+characteristics of that camera.
+
+The pipelines defined here tend to import other pipelines, including
+ingredient pipelines in the [_ingredients](./_ingredients) directory.
+To expand a pipeline YAML and resolve such imports for the purposes of
+visualizing it, the `pipetask build` command can be used.  For
+example, to visualize the verification of a bias for the [LATISS camera
+pipeline](https://github.com/lsst/cp_verify/blob/main/pipelines/Latiss/VerifyBias.yaml)
+pipeline, run:
+
+```bash
+pipetask build \
+-p $CP_VERIFY_DIR/pipelines/Latiss/VerifyBias.yaml \
+--show pipeline
+```

pipelines/_ingredients/README.md

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+# Pipeline Definition Ingredients
+
+This directory contains ingredient pipeline definition YAML files.
+The pipelines defined here are intended to be used as the basic blocks
+for calibration verification.  As such, they are not intended to be
+used directly by end-users for science purposes.
+
+Science ready pipeline definitions for specific cameras are located in
+the [pipelines](../pipelines) directory.