[Docs] Remove highlight directive from README

This works around GitHub rendering bug that renders "sh" in this place.

Also fixed whitespace around headline for consistency.

Reported-by: Dmitrii Kuvaiskii <dmitrii.kuvaiskii@intel.com>
Signed-off-by: Wojtek Porczyk <woju@invisiblethingslab.com>

README.rst

@@ -17,8 +17,6 @@ Gramine Library OS with Intel SGX Support
 .. |nbsp| unicode:: 0xa0
    :trim:
 
-.. highlight:: sh
-
 
 What is Gramine?
 ================
@@ -91,6 +89,7 @@ For bug reports and feature requests, `post an issue on our GitHub repository
 If you prefer emails, please send them to users@gramineproject.io
 (`public archive <https://groups.google.com/g/gramine-users>`__).
 
+
 Reporting security issues
 =========================