docs(faq): mention self-injection providers limitation

Author: micalevisk

content/faq/errors.md

@@ -6,7 +6,7 @@ During your development with NestJS, you may encounter various errors as you lea
 
 Probably the most common error message is about Nest not being able to resolve dependencies of a provider. The error message usually looks something like this:
 
-```text
+```bash
 Nest can't resolve dependencies of the <provider> (?). Please make sure that the argument <unknown_token> at index [<index>] is available in the <module> context.
 
 Potential solutions:
@@ -17,20 +17,23 @@ Potential solutions:
   })
 ```
 
-The most common culprit of the error, is not having the `provider` in the module's `providers` array. Please make sure that the provider is indeed in the `providers` array and following [standard NestJS provider practices](/fundamentals/custom-providers#di-fundamentals).
+The most common culprit of the error, is not having the `<provider>` in the module's `providers` array. Please make sure that the provider is indeed in the `providers` array and following [standard NestJS provider practices](/fundamentals/custom-providers#di-fundamentals).
 
 There are a few gotchas, that are common. One is putting a provider in an `imports` array. If this is the case, the error will have the provider's name where `<module>` should be.
 
-If you run across this error while developing, take a look at the module mentioned in the error message and look at its `providers`. For each provider in the `providers` array, make sure the module has access to all of the dependencies. Often times, `providers` are duplicated in a "Feature Module" and a "Root Module" which means Nest will try to instantiate the provider twice. More than likely, the module containing the `provider` being duplicated should be added in the "Root Module"'s `imports` array instead.
+If you run across this error while developing, take a look at the module mentioned in the error message and look at its `providers`. For each provider in the `providers` array, make sure the module has access to all of the dependencies. Often times, `providers` are duplicated in a "Feature Module" and a "Root Module" which means Nest will try to instantiate the provider twice. More than likely, the module containing the `<provider>` being duplicated should be added in the "Root Module"'s `imports` array instead.
+
+If the `<unknown_token>` above is the string `dependency`, you might have a circular file import. This is different from the [circular dependency](#circular-dependency-error) below because instead of  having providers depend on each other in their constructors, it just means that two files end up importing each other. A common case would be a module file declaring a token and importing a provider, and the provider import the token constant from the module file. If you are using barrel files, ensure that your barrel imports do not end up creating these circular imports as well.
 
-If the `unknown_token` above is the string `dependency`, you might have a circular file import. This is different from the [circular dependency](#circular-dependency-error) below because instead of  having providers depend on each other in their constructors, it just means that two files end up importing each other. A common case would be a module file declaring a token and importing a provider, and the provider import the token constant from the module file. If you are using barrel files, ensure that your barrel imports do not end up creating these circular imports as well.
+Also, make sure you didn't end up injecting the provider on itself because self-injections are not allowed on NetJS. When this happens, `<unknown_token>` will likely be equal to `<provider>`.
 
 #### Error on monorepos
 
 If you are in a monorepo setup, you may face the same error as above but for core provider called `ModuleRef` as a `<unknown_token>`:
 
-```text
-Nest can't resolve dependencies of the <provider> (?). Please make sure that the argument ModuleRef at index [<index>] is available in the <module> context.
+```bash
+Nest can't resolve dependencies of the <provider> (?).
+Please make sure that the argument ModuleRef at index [<index>] is available in the <module> context.
 ...
 ```