Add CI / CD Basics

CI-%2F-CD-Basics.md

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+
+Development only on feature branches, main branch must be assumed to be deployed.
+
+## 1. Before starting work, rebase current main into your feature branch
+
+So first, get the latest main branch to your computer
+```
+git checkout main
+git pull
+```
+
+Then, go back to your feature branch and rebase
+```
+git checkout feature-branch
+git rebase main
+```
+
+If that worked and conflicts are ruled out, push the rebased feature branch from your computer to the repo.
+```
+git push origin feature-branch --force-with-lease
+```
+
+
+
+However, if conflicts should occur, they need to be manually fixed and then added
+```
+git add <conflicted-file>
+git rebase --continue
+```
+
+
+## 2. Merging own feature branch 
+When a feature is finished and tested, it should be integrated into the main branch for deployment.
+So first, repeat the steps from 1 to make sure, the feature branch is compatible with the current main.
+
+Then, open a Pull Request in the UI. Ideally, someone else reviews it before the merge into main is completed.
+To avoid ugly merge commit statements, select 'Rebase and fast-forward'.
+
+If frequent PRs are made, it makes sense to select 'Squash and merge', so that small unspecific commits like "fixed typo" are bundled into
+a single, more descriptive commit message on main. The detailed commit history is still documented in the PR and on the feature branch.