[API] Valid POST request of a candidate added to the API TestPlan (#6601

)

In the API TestPlan, the example of a POST request to create a new candidate does not create a candidate. The new command line example creates a new candidate successfully.

    Resolves #6590

modules/api/test/TestPlan.md

@@ -33,10 +33,12 @@ See specification for the expected response format.
 
 
 #### Candidate creation - POST /candidates
-Candidate creation
-This is done by sending a POST request to /candidates with the required data. Note the usage of the Authorization header.
+Candidate creation is done by sending a POST request to /candidates with the required data. Note the usage of the Authorization header. For a candidate to be created, the candidate's information must also be included. The following command contains the minimal information necessary for the request to create a new candidate (see [docs](../../../docs/API/LorisRESTAPI_v0.0.3.md#30-candidate-api) for format instructions):
+
 ```bash
-~$ curl -H "Authorization: Bearer $token" https://<your-hostname>/api/v0.0.3/candidates -d '{see specs for content}'
+~$ curl -H "Authorization: Bearer $token" https://<your-hostname>/api/v0.0.3/candidates -d '{"Candidate":{"Project":"Rye","Site":"Montreal","DoB":"2019-01-31", "Sex":"Female"}}' 
 ```
 
+If the candidate is successfully created, the candidate's data is returned. For example, the previous example returns: `{"CandID":"872451","Project":"Rye","PSCID":"MTL185","Site":"Montreal","EDC":null,"DoB":"2019-01-31","Sex":"Female"}`
 
+Otherwise, an error message is returned. For example, the command `curl -H "Authorization: Bearer $token" https://<your-hostname>/api/v0.0.3/candidates -d ''` returns `{"error":"You are not affiliated with the candidate's site"}`