update master_doc in sphinx conf.py

docs/conf.py

@@ -14,7 +14,6 @@
 import sys
 sys.path.insert(0, os.path.abspath('../'))
 
-
 # -- Project information -----------------------------------------------------
 
 project = 'TextAttack'
@@ -24,6 +23,8 @@
 # The full version, including alpha/beta/rc tags
 release = '0.0.1'
 
+# Set master doc to `index.rst`.
+master_doc = 'index'
 
 # -- General configuration ---------------------------------------------------
 
@@ -61,4 +62,4 @@
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,
 # so a file named "default.css" will overwrite the builtin "default.css".
-html_static_path = ['_static']
+html_static_path = ['_static']