Docs: clarify defaultAssignment option, fix no-unneeded-ternary examp…

…les (#10874)

* Contradictions in no-unneeded-ternary documentation

See #10872

* Updated examples to more clearly reflect eslint behaviour.

* Update no-unneeded-ternary.md

docs/rules/no-unneeded-ternary.md

@@ -23,10 +23,10 @@ Here is an example:
 
 ```js
 // Bad
-var foo = bar ? bar : 1;
+foo(bar ? bar : 1);
 
 // Good
-var foo = bar || 1;
+foo(bar || 1);
 ```
 
 ## Rule Details
@@ -41,6 +41,8 @@ Examples of **incorrect** code for this rule:
 var a = x === 2 ? true : false;
 
 var a = x ? true : false;
+
+var a = f(x ? x : 1);
 ```
 
 Examples of **correct** code for this rule:
@@ -56,7 +58,7 @@ var a = x ? "Yes" : "No";
 
 var a = x ? y : x;
 
-var a = x ? x : 1;
+var a = x ? x : 1;  // Note that this is only allowed as it on the right hand side of an assignment; this type of ternary is disallowed everywhere else. See defaultAssignment option below for more details.
 ```
 
 ## Options
@@ -68,6 +70,8 @@ This rule has an object option:
 
 ### defaultAssignment
 
+The defaultAssignment option allows expressions of the form `x ? x : expr` (where `x` is any identifier and `expr` is any expression) as the right hand side of assignments (but nowhere else).
+
 Examples of additional **incorrect** code for this rule with the `{ "defaultAssignment": false }` option:
 
 ```js