Update docs/syntax/substitutions.md

Co-authored-by: Martijn Laarman <[email protected]>

Author: lcawl

docs/syntax/substitutions.md

@@ -24,7 +24,7 @@ subs:
 If a substitution is defined globally it may not be redefined (shaded) in a files `frontmatter`. 
 Doing so will result in a build error.
 
-To use the keywords in your files, surround them in curly brackets (`{{key}}`).
+To use the variables in your files, surround them in curly brackets (`{{variable}}`).
 
 ## Example