Minor README.md update

Author: Lucas-C

README.md

@@ -59,7 +59,11 @@ this hook only proceed to do so once, the first time an article is published.
 
 In order to do so, it uses a very simple and small cache that contains the list of all hyperlinks already parsed, per article `slug`.
 
-To remove a blog entry from cache, in order for the plugin to retry sending a linkback:
+To Llist successful linkbacks:
+
+    grep -B5 '"response"' pelican-plugin-linkbacks.json
+
+To remove a blog entry from cache, in order for the plugin to retry sending a linkback, using [`jq`](https://jqlang.org/):
 
     jq "del(.['$slug'])" pelican-plugin-linkbacks.json | sponge pelican-plugin-linkbacks.json
 
@@ -76,6 +80,8 @@ where `$CACHE_PATH` is [a Pelican setting](https://docs.getpelican.com/en/latest
   enforce HTTPS certificates verification when sending linkbacks
 - `LINKBACKS_REQUEST_TIMEOUT` (optional, in seconds, default: `3`) :
   time in seconds allowed for each HTTP linkback request before abandon
+- `LINKBACKS_IGNORED_URLS_PATTERN` (optional, default to: `artstation.com|deviantart.com|github.com|github.io|itch.io|readthedocs.io|youtube.com|wikipedia.org`)
+  list of hostnames to NOT try to send linkbacks to
 
 
 ## Manual execution