Add code changes to documentation workflow

We're creating generated documention, so we need to rebuild
on code changes.

Author: Pike

.github/workflows/documentation.yml

@@ -9,13 +9,15 @@ on:
     paths:
       - docs/**
       - fluent.*/docs/**
+      - fluent.*/fluent/**
       - fluent.*/setup.cfg
   pull_request:
     branches:
       - master
     paths:
       - docs/**
       - fluent.*/docs/**
+      - fluent.*/fluent/**
       - fluent.*/setup.cfg
 
 jobs: