!fixup: document NIXPKGS_REVIEW_PRE_BUILD_FILTER

Author: rmcgibbo

README.md

@@ -281,8 +281,23 @@ $ nixpkgs-review pr --skip-packages-regex 'linux_.*' 51292
 `-p`, `-P`, `--package-regex` and `--skip-package-regex` can be used together, in which case
 the matching packages will merged.
 
+<<<<<<< HEAD
 Full documentation for regex matching syntax can be found
 [here](https://docs.python.org/3/library/re.html#regular-expression-syntax).
+=======
+## Filter plugins
+
+After `nixpkgs-review` evaluates the set of changed packages but before it performs a build, it
+can interact with a set of plugins that can modify the set of packages. Such plugins should
+register themselves by setting the environment variable `NIXPKGS_REVIEW_PRE_BUILD_FILTER` to
+a colon-separated list of executables. Each executable called in order and piped a JSON
+structure containing `nixpkgs-review`'s internal representation of the package set, can modify
+it arbitrarily, and should return a new copy of the same JSON structure back on stdout.
+
+Note: this interface is UNSTABLE and we make NO BACKWARD OR FORWARD COMPATIBILITY PROMISES
+about the structure of the JSON between versions of nixpkgs-review.
+
+>>>>>>> ea1f67e (!fixup: document NIXPKGS_REVIEW_PRE_BUILD_FILTER)
 
 ## Running tests
 

nixpkgs_review/report.py

@@ -162,6 +162,8 @@ def upload_build_logs(self, github_client: GithubClient, pr: Optional[int]) -> N
                     )
                     pkg.log_url = gist["html_url"]
                 except urllib.error.HTTPError:
+                    # This is possible due to rate-limiting or a failure of that sort.
+                    # It should not be fatal.
                     traceback.print_exc(file=sys.stderr)
             else:
                 print(f"Log content for {pkg} was empty", file=sys.stderr)