Update operator docs (#683)

Include `++` list append, `xor`.

Polish table

Expand operator precedence.

book/operators.md

@@ -8,7 +8,9 @@ Nushell supports the following operators for common math, logic, and string oper
 | `-` | subtract |
 | `*` | multiply |
 | `/` | divide |
+| `//` | floor division |
 | `mod` | modulo |
+| `**` | exponentiation (power) |
 | `==` | equal |
 | `!=` | not equal |
 | `<` | less than |
@@ -20,27 +22,38 @@ Nushell supports the following operators for common math, logic, and string oper
 | `in` | value in list |
 | `not-in` | value not in list |
 | `not` | logical not |
-| `&&`, `and` | and two Boolean values |
-| `\|\|`, `or` | or two Boolean values |
-| `//` | floor division |
-| `**` | pow |
+| `&&`, `and` | and two Boolean expressions (short-circuits) |
+| `\|\|`, `or` | or two Boolean expressions (short-circuits) |
+| `xor` | exclusive or two boolean expressions |
 | `bit-or` | bitwise or |
 | `bit-xor` | bitwise xor |
 | `bit-and` | bitwise and |
 | `bit-shl` | bitwise shift left |
 | `bit-shr` | bitwise shift right |
 | `starts-with` | string starts with |
 | `ends-with` | string ends with |
+| `++` | append lists |
+
 
 Parentheses can be used for grouping to specify evaluation order or for calling commands and using the results in an expression.
 
 ## Order of Operations
 
-Math operations are evaluated in the follow order (from highest precedence to lowest):
+Operations are evaluated in the following order (from highest precedence to lowest):
 
 - Parentheses (`()`)
-- Multiply (`*`) and Divide (`/`) and Power (`**`)
+- Exponentiation/Power (`**`)
+- Multiply (`*`), Divide (`/`), Integer/Floor Division (`//`), and Modulo (`mod`) 
 - Add (`+`) and Subtract (`-`)
+- Bit shifting (`bit-shl`, `bit-shr`)
+- Comparison operations (`==`, `!=`, `<`, `>`, `<=`, `>=`), membership tests (`in`, `not-in`, `starts-with`, `ends-with`), regex matching (`=~`, `!~`), and list appending (`++`)
+- Bitwise and (`bit-and`)
+- Bitwise xor (`bit-xor`)
+- Bitwise or (`bit-or`)
+- Logical and (`&&`, `and`)
+- Logical xor (`xor`)
+- Logical or (`||`, `or`)
+- Assignment operations
 
 ```
 > 3 * (1 + 2)