document more exported environment variables

Signed-off-by: Nico Schottelius <nico@brief.schottelius.org>

doc/man/cdist-reference.text.sh

@@ -167,7 +167,7 @@ ENVIRONMENT VARIABLES
 ---------------------
 __explorer::
    Directory that contains all global explorers.
-   Available for: explorer
+   Available for: explorer, type explorer
 __manifest::
    Directory that contains the initial manifest.
    Available for: initial manifest
@@ -188,7 +188,7 @@ __object_name::
    Available for: type manifest, type explorer, type gencode
 __target_host::
    The host we are deploying to.
-   Available for: initial manifest, type manifest, type gencode
+   Available for: explorer, initial manifest, type explorer, type manifest, type gencode
 __type::
    Path to the current type.
    Available for: type manifest, type gencode