docs: Add documentation for upcoming MisleadingAndOr lint (#349)

This is going to be part of Luau 0.514

docs/_pages/lint.md

@@ -294,6 +294,7 @@ table.insert(t, 0, 42) -- table.insert uses index 0 but arrays are 1-based; did
 
 table.insert(t, #t+1, 42) -- table.insert will append the value to the table; consider removing the second argument for efficiency
 ```
+
 ## DuplicateCondition (24)
 
 When checking multiple conditions via `and/or` or `if/elseif`, a copy & paste error may result in checking the same condition redundantly. This almost always indicates a bug, so a warning is emitted when use of a duplicate condition is detected.
@@ -301,3 +302,18 @@ When checking multiple conditions via `and/or` or `if/elseif`, a copy & paste er
 ```lua
 assert(self._adorns[normID1] and self._adorns[normID1]) -- Condition has already been checked on column 8
 ```
+
+## MisleadingAndOr (25)
+
+In Lua, there is no first-class ternary operator but it can be emulated via `a and b or c` pattern. However, due to how boolean evaluation works, if `b` is `false` or `nil`, the resulting expression evaluates to `c` regardless of the value of `a`. Luau solves this problem with the `if a then b else c` expression; a warning is emitted for and-or expressions where the first alternative is `false` or `nil` because it's almost always a bug.
+
+```lua
+-- The and-or expression always evaluates to the second alternative because the first alternative is false; consider using if-then-else expression instead
+local x = flag and false or true
+```
+
+The code above can be rewritten as follows to avoid the warning and the associated bug:
+
+```lua
+local x = if flag then false else true
+```