move voice and tone back

Author: JuliaMongo

source/style-guide/style/index.txt

@@ -47,3 +47,4 @@ instructions for applying style conventions.
    /style-guide/style/titles-and-headings
    /style-guide/style/urls
    /style-guide/style/version
+   /style-guide/style/voice-and-tone

source/style-guide/writing/index.txt

@@ -23,7 +23,6 @@ and consistent, and that helps users accomplish their goals.
    /style-guide/writing/use-gender-neutral-pronouns
    /style-guide/writing/use-positive-statements
    /style-guide/writing/use-correct-punctuation
-   /style-guide/style/voice-and-tone
    /style-guide/writing/use-interjections-with-care
    /style-guide/writing/write-for-accessibility
    /style-guide/terminology/terms-for-global-audience