docs(minerr): fill in error message descriptions

Errors I've documented so far:
- `$injector:cdep`
- `$injector:itkn`
- `$injector:modulerr`
- `$injector:nomod`
- `$injector:pget`
- `$injector:unpr`
- `ng:areq`
- `ng:cpi`
- `ng:cpws`
- `ngModel:noass`

Closes #3430

2 files changed, 27 insertions, 4 deletions

diff --git a/docs/content/error/ngModel/noass.ngdoc b/docs/content/error/ngModel/noass.ngdoc
deleted file mode 100644
index c9fe6637..00000000
--- a/docs/content/error/ngModel/noass.ngdoc
+++ /dev/null
@@ -1,4 +0,0 @@
-@ngdoc error
-@name ngModel:noass
-@fullName Non-Assignable Expression
-@description
diff --git a/docs/content/error/ngModel/nonassign.ngdoc b/docs/content/error/ngModel/nonassign.ngdoc
new file mode 100644
index 00000000..33894c49
--- /dev/null
+++ b/docs/content/error/ngModel/nonassign.ngdoc
@@ -0,0 +1,27 @@
+@ngdoc error
+@name ngModel:nonassign
+@fullName Non-Assignable Expression
+@description
+
+This error occurs when expression the {@link api/ng.directive:ngModel ngModel} directive is bound to is a non-assignable expression.
+
+Examples using assignable expressions include:
+
+```
+<input ng-model="namedVariable">
+<input ng-model="myObj.someProperty">
+<input ng-model="indexedArray[0]">
+```
+
+Examples of non-assignable expressions include:
+
+```
+<input ng-model="foo + bar">
+<input ng-model="42">
+<input ng-model="'oops'">
+<input ng-model="myFunc()">
+```
+
+Always make sure that the expression bound via `ngModel` directive can be assigned to.
+
+For more information, see the {@link api/ng.directive:ngModel ngModel API doc}.