[ci] README

ci/README.md

+This directory is essentially a nix repository with some scripts.
+
+# Packages overview
+## batsched_local
+This is the current version of batsched (built from current file hierarchy).
+
+## batsim_pinned
+This is the current *reference* Batsim version for batsched.
+batsched should always work with this version.
+
+## batsim_dev
+This is the up-to-date Batsim version.
+batsched should work with this version.
+
+## test_deps_(pinned|local)
+The list of packages needed to run tests.
+This is meant to be used as a shell, not meant to be installed.
+
+## test_(pinned|local)
+A shell used to run tests. Essentially batsim_local + test_deps.
+Not meant to be installed either.
+
+# Useful commands
+In all the following examples, the current directory is expected to be
+batsched's root.
+
+## Building packages
+This can be done via `nix-build`. Result will be in `./result/`.
+Some examples:
+``` bash
+nix-build ./ci -A batsched_local
+nix-build ./ci -A batsim_pinned
+```
+
+## Install packages
+This is done via `nix-env`:
+``` bash
+nix-env -f ./ci -iA batsched_local
+nix-env -f ./ci -iA batsim_dev
+```
+
+To uninstall them, use `nix-env --uninstall`.
+
+## Get into a shell to build packages
+`nix-shell` is your friend here. Example:
+``` bash
+nix-shell ./ci -A batsched_local
+# your shell now has all batsched's build dependencies!
+# you can freely build the project (cmake, make...)
+```
+
+## Run the tests
+This is essentially "run the test script in the desired environment".
+``` bash
+# test current batsched with batsim_pinned:
+nix-shell ./ci -A test_pinned --command './ci/run-tests.bash'
+
+# or test with batsim_dev:
+nix-shell ./ci -A test_dev --command './ci/run-tests.bash'
+```