Add extra requirement "docs"

Author: eht16

.readthedocs.yaml

@@ -7,8 +7,8 @@ python:
   install:
     - method: pip
       path: .
-    - method: pip
-      path: sphinx-rtd-theme
+      extra_requirements:
+        - docs
 
 build:
   os: ubuntu-22.04

setup.py

@@ -43,6 +43,7 @@
     install_requires=['limits', 'pylogbeat', 'requests'],
     extras_require={
         'dev': ['django', 'flask'],
+        'docs': ['sphinx-rtd-theme'],
     },
     python_requires='>3.5',
     include_package_data=True,