Update v3.mdx

Author: mythz

content/docs/v3.mdx

@@ -306,6 +306,20 @@ __install__ = install
 llms --add
 ```
 
+Output:
+
+```
+Available extensions:
+  xmas             Example of utilizing the Extensions APIs to give llms.py some Christmas spirit
+  system_prompts   Enables and includes collection of awesome system prompts
+  core_tools       Essential tools for memory persistence, file operations, math expressions and code execution
+  duckduckgo       Add web search tool capabilities using Duck Duck Go
+
+Usage:
+  llms --add <extension>
+  llms --add <github-user>/<repo>
+```
+
 **Install an extension:**
 ```bash
 llms --add system_prompts