add gitlab build+deploy pipeline

.gitlab-ci.yml

+# Define the stages of this pipeline. Each job is associated with a stage.
+# Multiple jobs may be run in parallell during a stage. Dependant jobs
+# should run in different stages.
+stages:
+  - build
+  - deploy
+
+# Define a pipeline job for building the app
+build-job:
+  image: node:18 # Run this job in a docker image with node 18 installed
+  stage: build
+  script:
+    - cd app/
+    - npm install --production # Install nodejs production dependencies, skipping unnecessary
+                               # development dependencies
+    - npm run build # Build the app. Results stored in build/
+  artifacts:
+    paths:
+      - app/build/ # Save the build results for upcoming jobs
+
+# Define a pipeline job for deploying the build results. Must be named
+# "pages" to deploy to GitLab pages
+pages:
+  stage: deploy
+  script:
+    - export target="public/" # Location used by GitLab CI/CD
+    - mkdir $target
+    - cp -r app/build/* $target # Copy build results into target dir
+  artifacts:
+    paths:
+      - public # Save target dir

README.md

@@ -37,4 +37,9 @@ then run
 npm run build
 ````
 
-This should create the directory ```build```, containing the file ```index.html```. This file is the entry point for your web application. Depending on your environment (operating system, browser, etc), this file might be able to be opened by your browser.
+This should create the directory ```build```, containing the file ```index.html```. This file is the entry point for your web application. Depending on your environment (operating system, browser, etc), this file might be able to be opened by your browser.
\ No newline at end of file
+
+# Deployment
+The file ```.gitlab-ci.yml``` is used by GitLab to create [CI/CD jobs](https://docs.gitlab.com/ee/ci/). This can be used to build, test and deploy your app. The current ```.gitlab-ci.yml``` file is set to build and deploy the app when you push to any branch. The latest pipeline can be found on ```project/-/pipelines/latest``` (for example https://gitlab.liu.se/simto05/react-proof-of-concept/-/pipelines/latest). The deployed page can for this instance be found on https://simto05.gitlab-pages.liu.se/react-proof-of-concept/.
+
+A slight modification was made to the file ```package.json``` in directory ```app/``` because of GitLab CORS policy: the key ```homepage``` was set to "." to inform ```create-react-app``` that static files are located relative to the ```index.html``` file. This modification should work for most servers, but may vary with different setups.
\ No newline at end of file

app/package.json

@@ -2,6 +2,7 @@
   "name": "app",
   "version": "0.1.0",
   "private": true,
+  "homepage": ".",
   "dependencies": {
     "@testing-library/jest-dom": "^5.17.0",
     "@testing-library/react": "^13.4.0",