Fix buttons "edit this page", "create child page" and fix cover-block background on website (#3220)

* fix README.md add cvat.jpg

* fix button "edit this page" and "create this page"

* fixed documentation workflow (#3217)

* fix block cover on about page

* fix linter error

Co-authored-by: Andrey Zhavoronkov <andrey.zhavoronkov@intel.com>

site/assets/scss/_custom.scss

@@ -108,3 +108,9 @@
     border-radius: 8px;
     visibility: hidden;
 }
+
+/* cover block on about page */
+
+#td-cover-block-0 {
+    background-image: url("../images/background-about-page.jpg");
+}

site/config.toml

@@ -113,7 +113,7 @@ github_repo = "https://github.com/openvinotoolkit/cvat"
 github_project_repo = "https://github.com/openvinotoolkit/cvat"
 
 # Specify a value here if your content directory is not in your repo's root directory
-# github_subdir = ""
+github_subdir = "site"
 
 # Uncomment this if you have a newer GitHub repo with "main" as the default branch,
 # or specify a new value if you want to reference another branch in your GitHub links