docs(tree-sitter): document +tree-sitter flag in :lang readmes

Co-authored-by: Jeetaditya Chatterjee <jeetelongname@gmail.com>

modules/lang/sh/README.org

@@ -25,6 +25,9 @@ Fish script) to Doom Emacs.
   (supports bash-language-server).
 - +powershell ::
   Add syntax highlighting for Powershell script files (=.ps1= and =.psm1=).
+- +tree-sitter ::
+  Leverages tree-sitter for better syntax highlighting and structural text
+  editing. Requires [[doom-module:][:tools tree-sitter]].
  
 ** Packages
 - [[doom-package:][company-shell]] if [[doom-module:][:completion company]]