FEA: add W&B document

docs/source/user_guide/usage/use_weights _and_biases.rst

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+.. _header-n0:
+
+Use Weights & Biases
+====================
+
+RecBole allows visualizing configs and metrics of different experiments
+with W&B.
+
+If you are new to W&B, please set up it first.
+
+1. Start with a W&B account. `Create one now → <http://app.wandb.ai>`__
+
+2. Go to your project folder in your terminal and install library:
+   ``pip install wandb``
+
+3. Inside your project folder, log in W&B: ``wandb login`` `your API
+   key <https://wandb.ai/authorize>`__
+
+You can start W&B in RecBole by passing ``--log_wandb=True`` as command
+line argument, or use config dict. One can also turn ``log_wandb: True``
+in the ``overall.yaml`` file or provide it as external config file.
+
+**A Running Example:**
+
+You can run BPR model on ml-100k dataset with W&B as follow:
+
+.. code:: python
+
+   python run_recbole.py --log_wandb=True
+
+Then, go to your W&B project, you can see the following page, which
+shows the change of metrics during the training and validation in each
+epoch.
+
+.. figure:: https://raw.githubusercontent.com/leoleojie/cloudimg/master/data/202202191625104.png
+   :alt: 
+
+You can also check the detailed configuration information and evaluation
+metrics.
+
+.. figure:: https://raw.githubusercontent.com/leoleojie/cloudimg/master/data/202202191625985.png
+   :alt: 
+
+W&B also allows you to compare these metrics and configs across
+different experiments in the same project.
+
+.. figure:: https://raw.githubusercontent.com/leoleojie/cloudimg/master/data/202202191648205.png
+   :alt: 
+
+.. figure:: https://raw.githubusercontent.com/leoleojie/cloudimg/master/data/202202191701276.png
+   :alt: 
+
+You can select different projects to experiment by modifying
+``wandb_project`` parameter, which defaults to ``'recbole'``.
+
+For more details about W&B, please refer to `Weights & Biases -
+Documentation <https://docs.wandb.ai/>`__.