Update docs

Author: mattgodbolt

BuildingCompilers.md

@@ -4,28 +4,14 @@ Compiler Explorer builds its compilers using docker images. These images are eac
 
 ## Daily images
 
-There's an AWS instance (see `setup-builder.sh`) that is left shut down most of the time. It's used to build new
-compilers. Daily compilations are orchestrated via the admin node. It runs the `admin-daily-build.sh` on a daily
+Compilers are built using a Github workflow, running on our own builders, in the [compiler-workflows](https://github.com/compiler-explorer/compiler-workflows/) repo.
+
+Some legacy builds use a dedicated AWS instance (see `setup-builder.sh`) that is left shut down most of the time. These compilations are orchestrated via the admin node. It runs the `admin-daily-build.sh` on a daily
 schedule via cron (see `crontab.admin`). This script fires up the builder node, runs the various builds on it, and shuts down.
-The same crontab also updates the symlinks in `/opt/compiler-explorer` daily to point at the newest builds.
 
 ## New compilers
 
-New compilers are built by logging into the admin node (with `ce admin`), and then manually starting the build node (`ce builder start`).
-
-Then compilations can be run with commands like:
-
-```bash
-ce builder exec -- \
-  sudo docker run --rm --name clang.build \
-    -v/home/ubuntu/.s3cfg:/root/.s3cfg:ro compilerexplorer/clang-builder \
-    bash build.sh 6.0.0 s3://compiler-explorer/opt/
-```
-
-A clang build takes around 20 minutes.
-
-**Don't forget to shut the build node down with `ce builder stop` when you've finished!**
+New compilers can be built by triggering a Github action build - use the [Custom compiler build](https://github.com/compiler-explorer/infra/actions/workflows/bespoke-build.yaml) and then click "Run workflow".  A clang build takes around 20 minutes.
 
-Remember that after building a compiler you'll need to update the `update_compilers/install_compilers.sh` script
-to install it. And if you're updating an existing compiler, you'll need to do something like unpacking the
-compiler to the admin drive's `/tmp/` and then `rsync --delete-after -avz /tmp/compiler/ /opt/compiler-explorer/compiler/`.
+Remember that after building a compiler you'll need to update the [YAML configuration](bin/yaml)
+to install it.