Add first user guide

docs/index.rst

@@ -6,7 +6,8 @@ Welcome to earthkit-regrids's documentation
     This project is **BETA** and will be **Experimental** for the foreseeable future. Interfaces and functionality are likely to change, and the project itself may be scrapped. **DO NOT** use this software in any project/software that is operational.
 
 
-**earthkit-regrid** is a Python package for regridding.
+**earthkit-regrid** is a Python package for regridding. It features the :func:`interpolate` function to regrid values stored in an ndarray. At the moment, regridding is only available for a **pre-defined** set of source and target global grid combinations.
+
 
 .. toctree::
    :maxdepth: 1
@@ -15,6 +16,12 @@ Welcome to earthkit-regrids's documentation
 
    examples
 
+.. toctree::
+   :maxdepth: 1
+   :caption: Documentation
+
+   interpolate
+
 .. toctree::
    :maxdepth: 1
    :caption: Installation

docs/interpolate.rst

@@ -0,0 +1,21 @@
+interpolate
+==============
+
+.. py:function:: interpolate(values, source_gridspec, target_gridspec, matrix_version=None)
+
+    Interpolate the ``values`` from the ``source_gridspec`` onto the ``target_gridspec``.
+
+    :param values: the input values
+    :type values: ndarray
+    :param source_gridspec: the gridspec describing the grid that ``values`` are defined on
+    :type source_gridspec: dict
+    :param target_gridspec: the gridspec describing the target grid that ``values`` will be interpolated onto
+    :type target_gridspec: dict
+    :param matrix_version: the version of the pre-defined interpolation matrix to be used. None means the latest version will be used.
+    :type matrix_version: str
+    :rtype: ndarray
+
+Examples
+--------
+
+    - :ref:`/examples/interpolation.ipynb`

docs/requirements.txt

@@ -1,4 +1,5 @@
 # These are the requirements for readthedoc
+ipykernel
 docutils
 Pygments>=2.6.1
 Sphinx