Add informative comment on @NullUnmarked injections

[nimakarimipour]

Is your feature request related to a problem? Please describe.

It is not clear to the programmer why the element is annotated as @NullUnmarkd instead of @Nullable if the impact on downstream dependencies prevented annotator from adding @Nullable.

Describe the solution you'd like

Add informative comments on @NullUnmarked injections describing the impact of the annotated method locally and globally. With the format below as suggested by @msridhar:

// local for errors within the scope of the annotation, //non-local for errors outside annotation scope but within the same module, and //dependent module for errors in dependent modules

Describe alternatives you've considered
None.

Additional context
None.