Fix spacing (#4460)

"&emsp" currently show in doc, instead of tabs.

Author: YoniFeng

docs/cpp/left-shift-and-right-shift-operators-input-and-output.md

@@ -13,9 +13,9 @@ The bitwise shift operators are the right-shift operator (**`>>`**), which moves
 ## Syntax
 
 *`shift-expression`*:\
-&emsp *`additive-expression`*\
-&emsp *`shift-expression`* **`<<`** *`additive-expression`*\
-&emsp *`shift-expression`* **`>>`** *`additive-expression`*
+&emsp;*`additive-expression`*\
+&emsp;*`shift-expression`* **`<<`** *`additive-expression`*\
+&emsp;*`shift-expression`* **`>>`** *`additive-expression`*
 
 ## Remarks