Updated use cases in UG, fix typo in DG

docs/DeveloperGuide.md

@@ -470,6 +470,10 @@ Priorities: High (must have) - `* * *`, Medium (nice to have) - `* *`, Low (unli
     * 1b1. CodeConnect shows an error message.
       Use case ends.
 
+* 1d. Updated contact matches another existing contact
+    * 1b1. CodeConnect shows an error message.
+      Use case ends.
+
 **Use case: UC04 - View all contacts**
 
 **MSS**
@@ -556,6 +560,22 @@ Priorities: High (must have) - `* * *`, Medium (nice to have) - `* *`, Low (unli
 
       Use case ends.
 
+**Use case: UC09 - Viewing command history**
+
+**MSS**
+
+1. User selects command input.
+2. User requests to view previous or next command in history.
+3. CodeConnect retrieves the command from the command history.
+4. CodeConnect updates the contents of the command input.
+
+   Use case ends.
+
+**Extensions**
+
+* 3a. CodeConnect does not find any previous/next command in the command history.
+      Use case ends.
+
 *{More to be added}*
 
 ### Non-Functional Requirements

docs/UserGuide.md

@@ -206,7 +206,7 @@ Any commands you have run previously are saved in the command history, so that y
 Any edits you make to a command will be saved while navigating through your history, so you can go to a another command
 to refer to it, and then return back to your edited command to finish typing.
 
-**How to use:** Use the up and down arrow keys to navigate through your history while the command input is focused,
+**How to use:** Use the up and down arrow keys to navigate through your history while the command input is focused.
 
 #### Saving the data