Publish linux binaries via artifacts

Publish the most recently built linux binaries as artifacts. This makes
the wait shorter for users who just want to try copar quickly.

Also add a link to the artifacts in the readme

.gitlab-ci.yml

@@ -10,4 +10,12 @@ cache:
     - .stack-root/
 
 test:
-  script: stack --no-terminal --system-ghc --no-install-ghc --resolver lts-12.14 build --test --haddock --no-haddock-deps --bench --no-run-benchmarks
+  script:
+    - stack --no-terminal --system-ghc --no-install-ghc --resolver lts-12.14 build --copy-bins --test --haddock --no-haddock-deps --bench --no-run-benchmarks
+    - cp -r ~/.local/bin/ copar-linux-binaries
+  artifacts:
+    name: "${CI_PROJECT_NAME}-linux-binaries"
+    expire_in: 10 yrs
+    paths:
+    - copar-linux-binaries/
+

README.md

@@ -4,6 +4,8 @@
 
     stack build
 
+Alternatively, you can directly download the [latest binaries for linux](https://gitlab.cs.fau.de/i8/copar/-/jobs/artifacts/master/download?job=test).
+
 ## Running
 
 There isn't much to see, yet. To see pretty printed parse results,