QL: Update readme with alerts and actions information

Author: esbena

README.md

@@ -1,9 +1,20 @@
 # QL analysis support for CodeQL
 
-*Part of the May 2021 [code scanning hackathon](https://github.com/github/code-scanning-hackathon/issues/3).*
+- *Part of the May 2021 [code scanning hackathon](https://github.com/github/code-scanning-hackathon/issues/3).*
+- *Part of the October 2021 [code scanning hackathon](https://github.com/github/code-scanning-hackathon/issues/61).*
 
 Under development.
 
+## Viewing the alerts from github/codeql and github/codeql-go
+
+**TLDR: View https://github.com/github/codeql-ql/security/code-scanning?query=branch%3Anightly-changes-alerts periodically.**
+
+The [`nightly-changes-alerts` branch](https://github.com/github/codeql-ql/tree/nightly-changes-alerts) contains nightly snapshots of QL related code from [github/codeql](https://github.com/github/codeql) and [github/codeql-go](https://github.com/github/codeql-go). The corresponding [code-scanning alerts](https://github.com/github/codeql-ql/security/code-scanning?query=branch%3Anightly-changes-alerts) are from the [default query suite](https://github.com/github/codeql-ql/blob/main/ql/src/codeql-suites/ql-code-scanning.qls).
+
+The branch and alerts are updated every night by the [`nightly-changes.yml` workflow](https://github.com/github/codeql-ql/actions/workflows/nightly-changes.yml).
+
+Ideally, the scans would happen automatically as part of the PRs. That requires more coordination, and is tracked here: https://github.com/github/codeql-coreql-team/issues/1669.
+
 ## Building the tools from source
 
 [Install Rust](https://www.rust-lang.org/tools/install) (if using VSCode, you may also want the `rust-analyzer` extension), then run:
@@ -39,3 +50,15 @@ Run
 ```bash
 codeql test run <test-path> --search-path <repository-root-path>
 ```
+
+## GitHub Actions
+
+In addition to the above nightly scans of the known CodeQL repositories, the following Actions are of particular interest:
+
+- [`bleeding-codeql-analysis.yml`](https://github.com/github/codeql-ql/actions/workflows/bleeding-codeql-analysis.yml)
+  - runs on all PRs, displays how alerts for the known CodeQL repositories change as consequence of the PR
+  - the code from the known CodeQL repositories should be updated occasionally by running [`repo-tests/import-repositories.sh`](https://github.com/github/codeql-ql/blob/main/repo-tests/import-repositories.sh) locally, and creating a PR.
+  - produces an artifact built `ql` database in
+- [`build.yml`](https://github.com/github/codeql-ql/actions/workflows/build.yml)
+  - produces an artifact with the `ql` extractor and the `ql` query pack in
+