literal strings -> double bracketed strings

Turns out I misread `Programming in Lua` when I wrote this.

README.md

@@ -511,7 +511,7 @@ Since you have to pass strings to these functions, you often end up having to es
 vim.cmd('%s/\\Vfoo/bar/g')
 ```
 
-Literal strings are easier to use as they do not require escaping characters:
+Double bracketed strings are easier to use as they do not require escaping characters:
 
 ```lua
 vim.cmd([[%s/\Vfoo/bar/g]])

doc/nvim-lua-guide.txt

@@ -620,8 +620,8 @@ having to escape backslashes:
     vim.cmd('%s/\\Vfoo/bar/g')
 <
 
-Literal strings are easier to use as they do not require escaping
-characters:
+Double bracketed strings are easier to use as they do not require
+escaping characters:
 
     >
     vim.cmd([[%s/\Vfoo/bar/g]])