Update user guide with examples and fix typo

docs/UserGuide.md

@@ -94,15 +94,19 @@ Adds a student to the address book.
 
 Format: `addstu n/NAME p/PHONE_NUMBER e/EMAIL nn/NUSNET_ID a/ADDRESS [t/TAG]…​`
 
+* Add a student with the given details.
+* The name and nusnet id must be provided. And nusnet id must be unique.
+* All the remaining fields are optional. If not provided, a placeholder value will be used.
+
 <box type="tip" seamless>
 
 **Tip:** A person can have any number of tags (including 0)
 </box>
 
 Examples:
 * `addstu n/John Doe nn/e1234567 [p/98765432] [e/johnd@example.com] [a/John street, block 123, #01-01]`
-* `add n/Betsy Crowe nn/e01234567 t/friend e/betsycrowe@example.com a/Newgate Prison p/1234567 t/criminal`
-* `add n/Betsy Crowe nn/e01234567`
+* `addstu n/Betsy Crowe nn/e01234567 t/friend e/betsycrowe@example.com a/Newgate Prison p/1234567 t/criminal`
+* `addstu n/Betsy Crowe nn/e01234567`
 
 ### Listing all students : `list`
 

src/test/java/seedu/address/logic/parser/AddCommandParserTest.java

@@ -1,6 +1,6 @@
 package seedu.address.logic.parser;
 
-import static org.junit.jupiter.api.Assertions.assertAll;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 import static seedu.address.logic.Messages.MESSAGE_INVALID_COMMAND_FORMAT;
 import static seedu.address.logic.commands.CommandTestUtil.ADDRESS_DESC_AMY;
 import static seedu.address.logic.commands.CommandTestUtil.ADDRESS_DESC_BOB;
@@ -161,9 +161,8 @@ public void parse_optionalFieldsMissing_success() {
                         + NUSNET_DESC_AMY + ADDRESS_DESC_AMY,
                 new AddPersonCommand(expectedPerson2));
 
-        // only name and nusnet
-        assertAll("Optional fields missing", () ->
-                parser.parse(NAME_DESC_CHAD + NUSNET_DESC_CHAD)); // should not throw an error
+        // only name and nusnet provided
+        assertDoesNotThrow(() -> parser.parse(NAME_DESC_CHAD + NUSNET_DESC_CHAD));
     }
 
     @Test