docs(minErr): add minErr description for $compile:ctreq

Closes #3423

docs/content/error/compile/ctreq.ngdoc

@@ -2,3 +2,48 @@
 @name $compile:ctreq
 @fullName Missing Required Controller
 @description
+
+This error occurs when {@link api/ng.$compile template compiler} tries process the directive that specifies the `require` option in a {@link guide/directive#directivedefinitionobject directive definition},
+but the required directive controller is not present on the current DOM element (or its ancestor element, if `^` was specified).
+
+To resolve this error ensure that there is no typo in the required controller name and that the required directive controller is present on the current element.
+
+If the required controller is expected to be on a ancestor element, make ensure that you prefix the controller name in the `require` definition with `^`.
+
+If the required controller is optionally requested, use `?` or `^?` to specify that.
+
+
+Example of a directive that requires {@link api/ng.directive:ngModel ngModel} controller:
+```
+myApp.directive('myDirective', function() {
+  return {
+    require: 'ngModel',
+    ...
+  }
+}
+```
+
+This directive can then be used as:
+```
+<input ng-model="some.path" my-directive>
+```
+
+
+Example of a directive that optionally requires a {@link api/ng.directive:form form} controller from an ancestor:
+```
+myApp.directive('myDirective', function() {
+  return {
+    require: '^?form',
+    ...
+  }
+}
+```
+
+This directive can then be used as:
+```
+<form name="myForm">
+  <div>
+    <span my-directive></span>
+  </div>
+</form>
+```