Update instructions.md (#894)

Add tasks 3 and 4 to `instructions.md`

Author: depial

exercises/concept/high-school-sweetheart/.docs/instructions.md

@@ -27,3 +27,25 @@ Make sure to reuse `cleanupname` that you defined in the previous step and compo
 julia> firstletter("Jane")
 "J"
 ```
+
+## 3. Format the first letter as an initial
+
+Implement the `initial` method.
+It should take a name and return its first letter, uppercase, followed by a dot.
+Make sure to reuse `firstletter` that you defined in the previous step.
+
+```julia-repl
+initial("Robert")
+"R."
+```
+
+## 4. Put the initials inside of the heart
+
+Implement the `couple` method.
+It should take two names and return the initials with emoji hearts around.
+Make sure to reuse `initial` that you defined in the previous step.
+
+```julia-repl
+couple("Blake Miller", "Riley Lewis")
+"❤ B.  +  R. ❤"
+```