docs: add tip command inside the docs

Signed-off-by: Vincenzo Palazzo <[email protected]>

Author: vincenzopalazzo

docs/docs-book/src/using-coffee.md

@@ -113,8 +113,6 @@ Coffee tightly integrates with git, allowing you to easily upgrade your plugins
 coffee upgrade <repo_name>
 ```
 
-
-
 ### Listing all the plugins
 
 > ✅ Implemented
@@ -131,14 +129,23 @@ coffee list
 coffee show <plugin_name>
 ```
 
-## Searching for a plugin in remote repositories 
+### Searching for a plugin in remote repositories 
 
 > ✅ Implemented
 
 ```bash
 coffee search <plugin_name>
 ```
-_________
+
+### Tipping a plugin in Bitcoin
+
+> ✅ Implemented
+
+```
+coffee tip <plugin_name> <millisatoshi>
+```
+
+------
 ## Running coffee as a server
 
 To run Coffee as a server, you can use the `coffee_httpd` binary.