add robots, add variables, change docs

.env.example

@@ -0,0 +1,15 @@
+ALGOLIA_APP_ID=
+ALGOLIA_API_KEY=
+ALGOLIA_INDEX_NAME=
+
+GISCUS_DISCUSSION_CATEGORY=
+GISCUS_DISCUSSION_CATEGORY_ID=
+GISCUS_PROJECT_ID=
+
+GOOGLE_ANALYTICS_TAG_ID=
+
+ORGANIZATION_NAME=
+REPOSITORY_NAME=
+
+SITE_TITLE=
+SITE_URL=