Build tools: describe the exact commands to upload

Expand the docstring to mention what are the exact commands required to compile
and upload a new build tool version.

scripts/compile_version_upload_s3.sh

@@ -24,22 +24,33 @@
 #
 # To create a pre-compiled cached version and make it available on production,
 # **the script must be ran from a builder (build-default or build-large)** and
-# it's required to set the following environment variables for an IAM user with
-# permissions on ``readthedocs(inc)-build-tools-prod`` S3's bucket:
+# it's required to set several environment variables for an IAM user with
+# permissions on ``readthedocs(inc)-build-tools-prod`` S3's bucket. Also, note
+# that in production we need to install `aws` Python package to run the script.
+# We can do this in a different virtualenv to avoid collision with the builder's
+# code.
 #
-#   AWS_REGION
-#   AWS_ACCESS_KEY_ID
-#   AWS_SECRET_ACCESS_KEY
-#   AWS_BUILD_TOOLS_BUCKET
+# The whole process would be something like:
 #
-# Note that in production we need to install `aws` Python package to run the
-# script. We can do this in a different virtualenv to avoid collision with the
-# builder's code:
+#   ssh util01
+#   ssh `scaling status -s build-default -q | head -n 1`
 #
+#   sudo su - docs
+#   TOOL=python
+#   VERSION=3.10.0
+#
+#   cd /home/docs/checkouts/readthedocs.org/scripts
 #   virtualenv venv
 #   source venv/bin/activate
 #   pip install awscli==1.20.34
 #
+#   export AWS_REGION=...
+#   export AWS_ACCESS_KEY_ID=...
+#   export AWS_SECRET_ACCESS_KEY=...
+#   export AWS_BUILD_TOOLS_BUCKET=readthedocs(inc)-build-tools-prod
+#
+#   ./compile_version_upload.sh $TOOL $VERSION
+#
 #
 # USAGE
 #