docs: fix image links in `performance.md` (#29592)

* docs: fix image links in performance.md

Fixes https://github.com/electron/electron/issues/29580

Signed-off-by: Darshan Sen <[email protected]>

* Apply suggestions from code review

Co-authored-by: David Sanders <[email protected]>

Co-authored-by: David Sanders <[email protected]>

docs/tutorial/performance.md

@@ -120,9 +120,9 @@ file in the directory you executed it in. Both files can be analyzed using
 the Chrome Developer Tools, using the `Performance` and `Memory` tabs
 respectively.
 
-![performance-cpu-prof]
+![Performance CPU Profile][performance-cpu-prof]
 
-![performance-heap-prof]
+![Performance Heap Memory Profile][performance-heap-prof]
 
 In this example, on the author's machine, we saw that loading `request` took
 almost half a second, whereas `node-fetch` took dramatically less memory