[devhelp] docs: mention the API version

[Sébastien Wilmet <swilmet src gnome org>]

commit 2b15940485ba6eeee0411c6a5f9982d7912152a2
Author: Sébastien Wilmet <sw swilmet be>
Date:   Fri Jan 1 07:35:58 2021 +0100

    docs: mention the API version
    
    "For Devhelp 40.alpha (API version: 3)."

 docs/reference/devhelp-docs.xml | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/docs/reference/devhelp-docs.xml b/docs/reference/devhelp-docs.xml
index 928cb9b5..a0ca064e 100644
--- a/docs/reference/devhelp-docs.xml
+++ b/docs/reference/devhelp-docs.xml
@@ -10,7 +10,7 @@
   <bookinfo>
     <title>&package_name; &package_api_version; Reference Manual</title>
     <releaseinfo>
-      For &package_string;.
+      For &package_string; (API version: &package_api_version;).
     </releaseinfo>
   </bookinfo>