[docs] Clarify how to escape curly braces in samp text (#11987)

Co-authored-by: Bénédikt Tran <[email protected]>

doc/usage/restructuredtext/roles.rst

@@ -240,7 +240,10 @@ different style:
  :rst:role:`code` role instead.
 
  .. versionchanged:: 1.8
- Allowed to escape curly braces with backslash
+ Allowed to escape curly braces with double backslash. For example, in
+ ``:samp:`print(f"answer=\\{1+{variable}*2\\}")```, the part ``variable``
+ would be emphasized and the escaped curly braces would be displayed:
+ :samp:`print(f"answer=\\{1+{variable}*2\\}")`
 
 There is also an :rst:role:`index` role to generate index entries.