switch comments system to Giscus and update configuration settings

Author: JerryLinLinLin

_config.yml

@@ -107,7 +107,7 @@ toc: true
 #   shortname: 'jerrylinlinlin-github-io'   # Fill with your Disqus shortname. › https://help.disqus.com/en/articles/1717111-what-s-a-shortname
 
 comments:
-  active: # The global switch for posts comments, e.g., 'disqus'.  Keep it empty means disable
+  active: 'giscus' # The global switch for posts comments, e.g., 'disqus'.  Keep it empty means disable
   # The active options are as follows:
   disqus:
     shortname: 'jerrylinlinlin-github-io'
@@ -121,10 +121,10 @@ comments:
     repo_id: "MDEwOlJlcG9zaXRvcnkzODg3NzE4NjI="
     category: "General"
     category_id: "DIC_kwDOFywwFs4CYBvu"
-    mapping: # optional, default to 'pathname'
-    input_position: # optional, default to 'bottom'
+    mapping: 'pathname' # optional, default to 'pathname'
+    input_position: 'bottom' # optional, default to 'bottom'
     lang: # optional, default to the value of `site.lang`
-    reactions_enabled: # optional, default to the value of `1`
+    reactions_enabled: 1 # optional, default to the value of `1`
 
 # Self-hosted static assets, optional › https://github.com/cotes2020/chirpy-static-assets
 assets: