cookbooks/devel/pv: Update docs for hfl and hflc (#45)

- Add support for Diversion header
- Add support for PAI/PPI headers

docs/cookbooks/devel/pseudovariables.md

@@ -1129,6 +1129,9 @@ Implemented for:
 -   Record-Route
 -   Route
 -   Via
+-   Diversion
+-   P-Asserted-Identity
+-   P-Preferred-Identity
 
 For the rest of the headers works like **$hdr(name)**.
 
@@ -1170,6 +1173,9 @@ Implemented for:
 -   Record-Route
 -   Route
 -   Via
+-   Diversion
+-   P-Asserted-Identity
+-   P-Preferred-Identity
 
 For the rest of the headers works like **$hdrc(name)**.