Note major release

We require new software in the user's workflow environment, so we should
at least note this with a major release and provide instructions on how
to update their software.

docs/change_log.md

@@ -3,6 +3,19 @@
 As of April 2021, we use major version numbers (e.g. v2) to reflect backward incompatible changes to the workflow that likely require you to update your Nextstrain installation.
 We also use this change log to document new features that maintain backward compatibility, indicating these features by the date they were added.
 
+## v8 (19 Aug 2021)
+
+### Major changes
+
+- Annotate CDC-style epiweeks (e.g., "202019") as a color-by and filter option in Auspice JSONs ([#703](https://github.com/nextstrain/ncov/pull/703)). This functionality requires [the Python epiweeks package](https://pypi.org/project/epiweeks/). You will need to update your software environment to include this package, depending on how you run your builds.
+  - If you use the Nextstrain CLI with Docker, update the Docker image with `nextstrain update` and then run your builds as usual with `nextstrain build`.
+  - If you use the Nextstrain CLI without Docker, run your builds with `nextstrain build . --use-conda <...other options...>`.
+  - If you use Snakemake, run your builds with `snakemake --use-conda <...other options...>`.
+
+### Features
+
+- Update Conda environment to use [Augur 13.0.0](https://github.com/nextstrain/augur/blob/master/CHANGES.md#1300-17-august-2021) for an improved filtering experience ([#703](https://github.com/nextstrain/ncov/pull/703)).
+
 ## New features since last version update
 
  - 7 July 2021: Extensive changes to internally-used Nextstrain profiles.