[doc] Add an initial changelog

Attempt to document major changes that have been included since the
v1.20.1 release (back in 2020).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

CHANGELOG.md

@@ -0,0 +1,94 @@
+Changelog
+---------
+
+## [Unreleased]
+
+- Add support for UEFI Secure Boot via a dedicated iPXE shim.
+
+- Add support for LoongArch64 and RISC-V CPU architectures.
+
+- Add initial support for bare-metal operation on RISC-V.
+
+- Automatically download and boot `autoexec.ipxe` script if it exists.
+
+- Construct initrd-style CPIO archive for UEFI kernels.
+
+- Support loading a UEFI executable via a shim.
+
+- Support EAPoL and port authentication.
+
+- Support Link Layer Discovery Protocol (LLDP).
+
+- Support DHE and ECDHE key exchange mechanisms, GCM cipher mode of
+  operation, X25519, P-256, and P-384 elliptic curves, and ECDSA
+  certificates.
+
+- Remove support for TLS v1.0.
+
+- Support gzip decompression and compressed arm64 kernels.
+
+- Support decryption of CMS-encrypted files.
+
+- Use ACPI-provided system MAC address for USB NICs.
+
+- Support ECAM as a mechanism for accessing PCI configuration space.
+
+- Support keyboard maps.
+
+- Support dynamically created interactive forms.
+
+- Extend ConnectX driver to support ConnectX-3 devices.
+
+- Support error recovery on Broadcom NetXtreme-E devices.
+
+- Add Intel 100 Gigabit Ethernet device driver.
+
+- Add Marvell AQtion device driver.
+
+- Add Cadence Gigabit Ethernet MAC (GEM) device driver.
+
+- Add DesignWare MAC device driver.
+
+- Add DesignWare USB3 host controller device driver.
+
+- Add RDC R6040 device driver.
+
+- Add Google Virtual Ethernet (GVE) device driver.
+
+- Add EFI Managed Network Protocol device driver.
+
+- Add libslirp-based virtual NIC device driver.
+
+- Allow for reproducible builds.
+
+- Publish official images for AWS and Google Cloud.
+
+- Switch from Travis CI to GitHub Actions.
+
+## [v1.21.1] 2020-12-31
+
+- Create DMA API and support UEFI systems with the IOMMU enabled (for
+  drivers that have been updated to the new API).
+
+- Add iPhone USB tethering device driver.
+
+- Add USB mass storage device driver.
+
+- Add Broadcom NetXtreme-E device driver.
+
+- Enable stack cookies (for UEFI).
+
+## [v1.20.1] 2020-01-02
+
+- See commit log for significant changes in this and any earlier
+  releases.
+
+## [v1.0.0] 2010-02-02
+
+- Prehistoric version.
+
+
+[unreleased]: https://github.com/ipxe/ipxe/commits
+[v1.21.1]: https://github.com/ipxe/ipxe/releases/tag/v1.21.1
+[v1.20.1]: https://github.com/ipxe/ipxe/releases/tag/v1.20.1
+[v1.0.0]: https://github.com/ipxe/ipxe/releases/tag/v1.0.0