docs: provide QUDT annotation demonstration

Add a demonstration of the QUDT unit annotation process for EML records,
providing a practical guide for users.

docs/source/user/quickstart.rst

@@ -19,3 +19,55 @@ For the latest development version::
     $ pip install git+https://github.com/EDIorg/spinneret.git@development
 
 
+Adding QUDT Annotations to an EML File
+---------------------------------------
+
+.. code-block:: python
+
+    from spinneret.datasets import get_example_eml_dir
+    from spinneret.workbook import create, delete_unannotated_rows
+    from spinneret.utilities import load_eml, write_eml
+    from spinneret.annotator import add_qudt_annotations_to_workbook, \
+        annotate_eml, get_qudt_annotation
+
+Starting with an example EML file without QUDT annotations
+
+.. code-block:: python
+
+    eml_file = get_example_eml_dir() + "/edi.3.9.xml"
+
+We initialize a "workbook" to store the annotations in a tabular format. The
+workbook contents are later added to the EML file as annotation elements.
+
+.. code-block:: python
+
+    workbook = create(eml_file, elements=["attribute"])
+
+A QUDT workbook "annotator" then searches through the EML for data entity
+attributes with EML standard units (or custom units) that may be mapped to
+QUDT equivalents via https://vocab.lternet.edu/webservice/unitsws.php, and adds
+successful matches to the workbook.
+
+.. code-block:: python
+
+    eml = load_eml(eml_file)
+    workbook = add_qudt_annotations_to_workbook(workbook, eml)
+    workbook = delete_unannotated_rows(workbook)  # a little cleanup
+
+We can now transfer the annotations from the workbook to the EML and write it
+to file.
+
+.. code-block:: python
+
+    annotated_eml = annotate_eml(eml_file, workbook)
+    output_path = "/Users/me/Data/edi.3.9.xml"  # or wherever you'd like
+    write_eml(annotated_eml, output_path)
+
+If you prefer a more rudimentary implementation, you can get QUDT label and URI
+for specified input text.
+
+.. code-block:: python
+
+    get_qudt_annotation("degree")
+
+    >>> [{'label': 'Degree', 'uri': 'http://qudt.org/vocab/unit/DEG'}]