changelog: add more newly-accepted urls

I encountered some problematic URLs,
and was delighted to see that they were already fixed.
I figured I may as well add them to the changelog.

For the record, URLs with no path used to be rejected.
That is arguably correct, but command line git accepts them.

URLs with a path of / and a non-standard port
used to have their port completely ignored!

docs/changelog.md

@@ -27,8 +27,10 @@ v0.28 + 1
 
 ### Changes or improvements
 
-* libgit2 can now correctly cope with URLs where the host contains a colon
-  but a port is not specified.  (eg `http://example.com:/repo.git`).
+* libgit2 now correctly handles more URLs, such as
+  `http://example.com:/repo.git` (colon but no port),
+  `http://example.com` (no path),
+  and `http://example.com:8080/` (path is /, nonstandard port).
 
 * A carefully constructed commit object with a very large number
   of parents may lead to potential out-of-bounds writes or