Add warning about using __tera_context

Author: c-git

content/misc/tera.md

@@ -1,12 +1,15 @@
 +++
 title = "Tera Guide"
 date=2023-10-27
-updated = 2025-04-26
+updated = 2026-02-19
 taxonomies = { tags = ["Misc"] }
 +++
 
 ## Get everything in context
 
+This is useful for debugging.
+But be warned it includes all the content of the site so on large sites it is VERY big.
+
 ```
 {{ __tera_context }}
 ```