doc/rf: Import Client class into root, update docs

Author: effigies

docs/api.rst

@@ -5,5 +5,6 @@ Information on specific functions, classes, and methods.
 .. toctree::
 
    api/templateflow.cli
+   api/templateflow.client
    api/templateflow.api
    api/templateflow.conf

templateflow/__init__.py

@@ -40,12 +40,14 @@
     del PackageNotFoundError
 
 from templateflow import api
+from templateflow.client import TemplateFlowClient
 from templateflow.conf import update
 
 __all__ = [
     '__copyright__',
     '__packagename__',
     '__version__',
+    'TemplateFlowClient',
     'api',
     'update',
 ]

templateflow/api.py

@@ -20,14 +20,30 @@
 #
 #     https://www.nipreps.org/community/licensing/
 #
-"""TemplateFlow's Python Client."""
-
-__all__ = [
-    'get',
-    'ls',
-    'get_metadata',
-    'get_citations',
-]
+"""TemplateFlow's Python Client.
+
+``templateflow.api`` provides a global, high-level interface to query the TemplateFlow archive.
+
+There are two methods to initialize a client:
+
+    >>> from templateflow import api as client
+
+    >>> from templateflow import TemplateFlowClient
+    >>> client = TemplateFlowClient()
+
+The latter method allows additional configuration for the client,
+while ``templateflow.api`` is only configurable through environment variables.
+
+.. autofunction:: get
+
+.. autofunction:: ls
+
+.. autofunction:: templates
+
+.. autofunction:: get_metadata
+
+.. autofunction:: get_citations
+"""
 
 from .client import TemplateFlowClient
 from .conf import _cache