Add license info to the docs

Author: domdfcoding

.github/workflows/docs_test_action.yml

@@ -33,4 +33,4 @@ jobs:
         with:
           pre-build-command: python -m pip install tox
           docs-folder: "doc-source/"
-          build-command: "tox -e docs -- "
+          build-command: "tox -e docs -- -W "

doc-source/index.rst

@@ -123,6 +123,7 @@ coverage_pyver_pragma
 
 .. end shields
 
+
 Contents
 ----------
 
@@ -142,7 +143,7 @@ Contents
 	syntax
 	api
 	Source
-
+	license
 
 .. sidebar-links::
 	:caption: Links

repo_helper.yml

@@ -15,6 +15,7 @@ min_coverage: 95
 sphinx_html_theme: furo
 python_deploy_version: 3.6
 preserve_custom_theme: true
+docs_fail_on_warning: true
 
 conda_channels:
   - conda-forge