[Docs] Clarify `html` encoder in highlighting.asciidoc
The previous description was a bit confusing because the pre/post tags used for highlighting are not escaped, the rest of the content is.
@@ -145,8 +145,9 @@ You can specify the locale to use with `boundary_scanner_locale`.
boundary_scanner_locale:: Controls which locale is used to search for sentence
and word boundaries.
-encoder:: Indicates if the highlighted text should be HTML encoded:
-`default` (no encoding) or `html` (escapes HTML highlighting tags).
+encoder:: Indicates if the snippet should be HTML encoded:
+`default` (no encoding) or `html` (HTML-escape the snippet text and then
+insert the highlighting tags)
fields:: Specifies the fields to retrieve highlights for. You can use wildcards
to specify fields. For example, you could specify `comment_*` to
