Update DG storage size.

Update DG testing instructions.
Update DG UI diagram.

Author: laney0808

docs/DeveloperGuide.md

@@ -610,15 +610,19 @@ testers are expected to do more *exploratory* testing.
 ### Adding a person
 
 1. Adding a person while all persons are being shown.
-   1. Prerequisites: List all persons using the `list` command. Multiple persons in the list.
+   1. Prerequisites: 
+      2. List all persons using the `list` command. Multiple persons in the list.
+      2. The person with NRIC `S1234567A` is not already created in the system.
+      3. The person with NRIC `T0234567C` is already created in the system.
    1. Test case: `create n/Alice Tan ic/S1234567A dob/1990-01-01 hp/12345678 a/123, Jurong West Ave 6, #08-111 s/F st/PENDING`<br>
       Expected: A new person is added to the list. The result panel shows the details of the new person.
    1. Test case: `create n/Bob Tan ic/T0234567C dob/1990-01-01 hp/12345678 a/123, Jurong West Ave 6, #08-111 s/M st/PENDING`<br>
       Expected: A new person is not added to the list. The result panel shows an error message, indicating that the person already exists in the system.
    1. Test case: `create n/Charlie Tan ic/S1234567A`<br>
       Expected: A new person is not added to the list. The result panel shows an error message, indicating that the command format is invalid.
 2. Adding a person while only some persons are being shown
-   1. Prerequisites: show only 1 person's details using the `find n/alex` command. One person is shown in the list.
+   1. Prerequisites: 
+   2. Show only 1 person's details using the `find n/alex` command. One person is shown in the list.
    1. Test case: `create n/Bob Tan ic/T0234567C dob/1990-01-01 hp/12345678 a/123, Jurong West Ave 6, #08-111 s/M st/PENDING`<br>
       Expected: A new person is not added to the list. The result panel shows an error message, indicating that the person already exists in the system.
 ### Deleting a person