bip3: Add and backfill Changelog section

The Version header is omitted at this time, as it is not permitted under BIP 2.

Author: murchandamus

bip-0003.md

@@ -156,7 +156,7 @@ appear in the following order. Headers marked with "\*" are optional. All other
   discussion threads on other platforms. Entries take the format "yyyy-mm-dd: URL", e.g., `2009-01-09:
   https://www.mail-archive.com/[email protected]/msg10142.html`, using the date and URL of the start of the
   conversation. Multiple discussions should be listed on separate lines.
-* Version — The current version number of this BIP. See the [Changelog](#changelog) section below.
+* Version — The current version number of this BIP. See the [Changelog](#changelog-section-and-version-header) section below.
 * Requires — A list of existing BIPs the new proposal depends on. If multiple BIPs
   are required, they should be listed in one line separated by a comma and space (e.g., "1, 2").
 * Replaces[^proposes-to-replace] — BIP authors may put the numbers of one or more prior BIPs in the Replaces header to recommend that their
@@ -331,7 +331,7 @@ if the prior attempt had been assigned a number, the new BIP will generally be a
 obvious that the new attempt directly continues work on the same idea, it may be reasonable to return the
 Closed BIP to Draft status.
 
-### Changelog
+### Changelog Section and Version Header
 
 To help implementers understand updates to a BIP, any changes after it has reached Complete must be tracked with version,
 date, and description in a Changelog section sorted by most recent version first. The version number is inspired by semantic versioning (MAJOR.MINOR.PATCH).
@@ -599,6 +599,26 @@ The Superseded-By header is replaced with the Proposed-Replacement header in all
 Existing BIPs retain their license terms unchanged.
 The License and License-Code headers of BIPs are updated to express those terms using SPDX License Expressions.
 
+## Changelog
+
+* __1.4.0__ (2025-12-09):
+    * Revert AI guidance, add Changelog section, broaden reference implementation formats, move Type header responsibility to authors, other editorial changes
+* __1.3.1__ (2025-11-10):
+    * Reiterate that numbers are assigned by BIP Editors in pull requests
+* __1.3.0__ (2025-10-22):
+    * Restrict use of AI/LLM tools, require original work.
+* __1.2.1__ (2025-09-19):
+    * Clarify that idea should be discussed on dedicated mailing list thread
+* __1.2.0__ (2025-09-19):
+    * Rename Created header to Assigned to clarify that it holds the date of number assignment
+* __1.1.0__ (2025-07-18):
+    * Switch to SPDX License Expressions, drop License-Code header, and make editorial changes to BIP Licensing section.
+* __1.0.1__ (2025-06-27):
+    * Improve description of acceptance, purpose of the BIPs repository, when Draft BIPs can be closed due to not
+      making progress, and make other minor improvements to phrasing.
+* __1.0.0__ (2025-03-18):
+    * Complete planned work and move to Proposed.
+
 ## Copyright
 
 This BIP is licensed under the [BSD-2-Clause License](https://opensource.org/licenses/BSD-2-Clause). Some content was