Add autosetbuffer script howto

documentation/weechat.markdown

@@ -138,8 +138,17 @@ To enable highlights, when a user sends a message important for all users like `
 
 ### Set extra highlights on buffer
 
-You can force highlight using a regular expression with the buffer property "highlight_regex". For example to force the highlight on all messages in the current buffer:
+You can force highlight using a regular expression with the buffer property `highlight_regex`. For example to force the highlight on all messages in the current buffer:
 
 ```
 /buffer set highlight_regex .*
 ```
+
+The buffer property `highlight_regex` is not saved in configuration.
+You can easily save it with the script `buffer_autoset.py`:
+
+```
+/script install buffer_autoset.py
+/help autosetbuffer
+/autosetbuffer add irc.phys.#isgphys highlight_regex .*
+```