docs: Mark heading in migration guide
authorAntónio Fernandes <antoniojpfernandes@gmail.com>
Sun, 14 Feb 2021 15:20:54 +0000 (15:20 +0000)
committerAntónio Fernandes <antoniojpfernandes@gmail.com>
Sun, 14 Feb 2021 15:20:54 +0000 (15:20 +0000)
commita810f600bfa3ed8340ce8e1799257e7cfa7d2aeb
treee05e5386d8eef1e0e97fb63b57c8cd1e0204e127
parent0222d389eefe5ec5cef6282912b78ebac791cc40
docs: Mark heading in migration guide

This heading was missing from the index because it was not marked as one
docs/reference/gtk/migrating-3to4.md