Add documentation for Camel 3.4.x the LTS (#407)

diff --git a/antora-playbook.yml b/antora-playbook.yml
index bcb26e3..0fbb761 100644
--- a/antora-playbook.yml
+++ b/antora-playbook.yml
@@ -18,6 +18,19 @@
         - core/camel-xml-jaxp/src/main/docs
         # main components doc
         - docs/components
+        
+    - url: git@github.com:apache/camel.git
+      branches: camel-3.4.x
+      start_paths:
+        # manual
+        - docs/user-manual
+        # eip
+        - core/camel-core-engine/src/main/docs
+        # languages
+        - core/camel-core-languages/src/main/docs
+        - core/camel-xml-jaxp/src/main/docs
+        # main components doc
+        - docs/components
 
     - url: git@github.com:apache/camel.git
       branches: camel-3.3.x