Rename CI/CD platform to CI environment

As discussed here:
https://github.com/dagger/dagger.io/issues/38#issuecomment-1057469048

Signed-off-by: Gerhard Lazu <gerhard@lazu.co.uk>

docs/getting-started/1201-ci-environment.md

@@ -0,0 +1,36 @@
+---
+slug: /1201/ci-environment
+displayed_sidebar: europa
+---
+
+# From local dev to CI environment
+
+import Tabs from '@theme/Tabs'; import TabItem from '@theme/TabItem';
+
+<Tabs defaultValue="github-actions"
+groupId="ci-environment"
+values={[
+{label: 'GitHub Actions', value: 'github-actions'},
+{label: 'CircleCI', value: 'circleci'},
+{label: 'GitLab', value: 'gitlab'},
+]}>
+
+<TabItem value="github-actions">
+
+Since Dagger early access required a GitHub account, GitHub Actions seems like a reasonable starting point.
+
+</TabItem>
+
+<TabItem value="circleci">
+
+If you would like us to document this CI environment next, mention it here: [dagger#1677](https://github.com/dagger/dagger/discussions/1677)
+
+</TabItem>
+
+<TabItem value="gitlab">
+
+If you would like us to document this CI environment next, mention it here: [dagger#1677](https://github.com/dagger/dagger/discussions/1677)
+
+</TabItem>
+
+</Tabs>