Update ReadTheDocs branch used (#524)

* Update ReadTheDocs branch used

* add logo
pydata/pydata-sphinx-theme#1094

Author: guilhermeleobas

doc/conf.py

@@ -88,11 +88,15 @@
 html_theme_options = {
     "github_url": "https://github.com/xnd-project/rbc",
     "use_edit_page_button": True,
+   "logo": {
+      "image_light": html_logo,
+      "image_dark": html_logo,
+   }
 }
 
 html_context = {
     "github_user": "xnd-project",
     "github_repo": "rbc",
-    "github_version": "master",
+    "github_version": "main",
     "doc_path": "doc",
 }