docs: Add more feature truth tables

These are much easier to understand at a glance than free-form text.

docs/yaml/objects/feature.yaml

@@ -27,11 +27,11 @@ methods:
   description: |
     Returns the feature, with `'auto'` converted to `'disabled'` if value is true.
 
-    | Feature / Condition | `value = true` | `value = false` |
-    | ------------------- | -------------- | --------------- |
+    | Feature  | `value = true` | `value = false` |
+    | -------- | -------------- | --------------- |
+    | Auto     | Disabled       | Auto            |
     | Enabled  | Enabled        | Enabled         |
     | Disabled | Disabled       | Disabled        |
-    | Auto                | Disabled       | Auto            |
 
   posargs:
     value:
@@ -44,11 +44,11 @@ methods:
   description: |
     Returns the feature, with `'auto'` converted to `'enabled'` if value is true.
 
-    | Feature / Condition | `value = true` | `value = false` |
-    | ------------------- | -------------- | --------------- |
+    | Feature  | `value = true` | `value = false` |
+    | -------- | -------------- | --------------- |
+    | Auto     | Enabled        | Auto            |
     | Enabled  | Enabled        | Enabled         |
     | Disabled | Disabled       | Disabled        |
-    | Auto                | Enabled        | Auto            |
 
   posargs:
     value:
@@ -63,6 +63,12 @@ methods:
     `'enabled'` and the value is false; a disabled feature if the object
     is `'auto'` or `'disabled'` and the value is false.
 
+    | Feature  | `value = true` | `value = false` |
+    | -------- | -------------- | --------------- |
+    | Auto     | Auto           | Disabled        |
+    | Enabled  | Enabled        | Error           |
+    | Disabled | Disabled       | Disabled        |
+
   example: |
     `require` is useful to restrict the applicability of `'auto'` features,
     for example based on other features or on properties of the host machine:
@@ -94,6 +100,12 @@ methods:
     `'disabled'` and the value is true; an enabled feature if the object
     is `'auto'` or `'enabled'` and the value is true.
 
+    | Feature  | `value = true` | `value = false` |
+    | -------- | -------------- | --------------- |
+    | Auto     | Enabled        | Auto            |
+    | Enabled  | Enabled        | Enabled         |
+    | Disabled | Error          | Disabled        |
+
   example: |
     `enable_if` is useful to restrict the applicability of `'auto'` features,
     particularly when passing them to [[dependency]]:
@@ -122,6 +134,12 @@ methods:
     `'enabled'` and the value is true; a disabled feature if the object
     is `'auto'` or `'disabled'` and the value is true.
 
+    | Feature  | `value = true` | `value = false` |
+    | -------- | -------------- | --------------- |
+    | Auto     | Disabled       | Auto            |
+    | Enabled  | Error          | Enabled         |
+    | Disabled | Disabled       | Disabled        |
+
     This is equivalent to `feature_opt.require(not condition)`, but may make
     code easier to reason about, especially when mixed with `enable_if`