Add change log and migration guide

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/ChangeLog.d/remove-enable-weak-ciphersuites.txt b/ChangeLog.d/remove-enable-weak-ciphersuites.txt
new file mode 100644
index 0000000..97f63eb
--- /dev/null
+++ b/ChangeLog.d/remove-enable-weak-ciphersuites.txt
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+Removals
+   * Remove MBEDTLS_ENABLE_WEAK_CIPHERSUITES configuration option. Fixes #4416.