docs: update structure and add more doc on s3 backend

Signed-off-by: Tiexin Guo <guotiexin@gmail.com>

docs/core-concepts/config.md

@@ -1,4 +1,4 @@
-# Config
+# DevStream Configuration
 
 DevStream uses YAML files to describe your DevOps toolchain configuration.
 

docs/core-concepts/stateconfig.md

@@ -1,13 +1,13 @@
-# The State Section in the Main Config
+# State Configuration
 
 In the main config, we can specify which "backend" to use to store DevStream state.
 
-We support the following types of backend:
+A backend is where to actually store the state file. We support the following types of backend:
 
 - local
 - s3
 
-## Local backend config example:
+## Local Backend
 
 ```yaml
 varFile: variables-gitops.yaml
@@ -22,7 +22,9 @@ state:
 
 The `stateFile` under the `options` section is mandatory for local backend.
 
-## S3 backend config example:
+## S3 Backend
+
+TL;DR: see the config example:
 
 ```yaml
 varFile: variables-gitops.yaml
@@ -37,4 +39,124 @@ state:
     key: devstream.state
 ```
 
-The `bucket`, `region`, and `key` under the `ptions` section are all mandatory fields for s3 backend.
+_Note: the `bucket`, `region`, and `key` under the `ptions` section are all mandatory fields for s3 backend._
+
+From release [v0.6.0](https://github.com/devstream-io/devstream/releases/tag/v0.6.0), using AWS S3 to store DevStream state is supported.
+
+More on configuring state [here](./stateconfig.md).
+
+In short, we can use the "backend" keyword to specify where to store the state: either locally or in an S3 bucket. If S3 is used, we need to specify the bucket, region, and the S3 key as well.
+
+### Config File Using S3 Backend
+
+`config.yaml`:
+
+```yaml
+varFile: variables-gitops.yaml
+
+toolFile: tools-gitops.yaml
+
+state:
+  backend: s3
+  options:
+    bucket: devstream-test-remote-state
+    region: ap-southeast-1
+    key: devstream.state
+```
+
+`variables-gitops.yaml`:
+
+```yaml
+githubUsername: IronCore864
+repoName: dtm-test-go
+defaultBranch: main
+
+dockerhubUsername: ironcore864
+
+argocdNameSpace: argocd
+argocdDeployTimeout: 5m
+```
+
+`tools-gitops.yaml`:
+
+```yaml
+tools:
+- name: github-repo-scaffolding-golang
+  instanceID: default
+  options:
+    owner: [[ githubUsername ]]
+    org: ""
+    repo: [[ repoName ]]
+    branch: [[ defaultBranch ]]
+    image_repo: [[ dockerhubUsername ]]/[[ repoName ]]
+```
+
+### Using the S3 Backend
+
+Before reading on, now is a good time to check if you have configured your AWS related environment variables correctly or not.
+
+For macOS/Linux users, do:
+
+```shell
+export AWS_ACCESS_KEY_ID=ID_HERE
+export AWS_SECRET_ACCESS_KEY=SECRET_HERE
+export AWS_DEFAULT_REGION=REGION_HERE
+```
+
+For more information, see the [official document here](https://docs.aws.amazon.com/cli/latest/userguide/cli-chap-configure.html).
+
+Then let's run `dtm apply`:
+
+```shell
+tiexin@mbp ~/work/devstream-io/devstream $ ./dtm apply
+2022-05-30 17:07:59 ℹ [INFO]  Apply started.
+2022-05-30 17:07:59 ℹ [INFO]  Using dir <.devstream> to store plugins.
+2022-05-30 17:07:59 ℹ [INFO]  Using s3 backend. Bucket: devstream-test-remote-state, region: ap-southeast-1, key: devstream.state.
+2022-05-30 17:08:00 ℹ [INFO]  Tool (github-repo-scaffolding-golang/default) found in config but doesn't exist in the state, will be created.
+Continue? [y/n]
+Enter a value (Default is n): y
+
+2022-05-30 17:08:08 ℹ [INFO]  Start executing the plan.
+2022-05-30 17:08:08 ℹ [INFO]  Changes count: 1.
+2022-05-30 17:08:08 ℹ [INFO]  -------------------- [  Processing progress: 1/1.  ] --------------------
+2022-05-30 17:08:08 ℹ [INFO]  Processing: (github-repo-scaffolding-golang/default) -> Create ...
+2022-05-30 17:08:12 ℹ [INFO]  The repo dtm-test-go has been created.
+2022-05-30 17:08:29 ✔ [SUCCESS]  Tool (github-repo-scaffolding-golang/default) Create done.
+2022-05-30 17:08:29 ℹ [INFO]  -------------------- [  Processing done.  ] --------------------
+2022-05-30 17:08:29 ✔ [SUCCESS]  All plugins applied successfully.
+2022-05-30 17:08:29 ✔ [SUCCESS]  Apply finished.
+```
+
+As we can see from the output, the S3 backend is used, and it also shows the bucket and key you are using, and in which region this bucket lives.
+
+After `apply`, let's download the state file from S3 and check it out:
+
+```shell
+tiexin@mbp ~/work/devstream-io/devstream $ aws s3 cp s3://devstream-test-remote-state/devstream.state .
+```
+
+And if we open the downloaded file, we will see something similar to the following:
+
+```yaml
+github-repo-scaffolding-golang_default:
+  name: github-repo-scaffolding-golang
+  instanceid: default
+  dependson: []
+  options:
+    branch: main
+    image_repo: ironcore864/dtm-test-go
+    org: ""
+    owner: IronCore864
+    repo: dtm-test-go
+  resource:
+    org: ""
+    outputs:
+      org: ""
+      owner: IronCore864
+      repo: dtm-test-go
+      repoURL: https://github.com/IronCore864/dtm-test-go.git
+    owner: IronCore864
+    repoName: dtm-test-go
+```
+
+which is exactly the same as if we were using the local backend to store state.

mkdocs.yml

@@ -80,7 +80,13 @@ nav:
   - Overview: .
   - understanding_the_basics*.md
   - quickstart*.md
-  - Core Concepts: core-concepts/
+  - Core Concepts:
+    - core-concepts/core-concepts*.md
+    - core-concepts/config*.md
+    - core-concepts/stateconfig*.md
+    - core-concepts/variable*.md
+    - core-concepts/dependencies*.md
+    - core-concepts/output*.md
   - Commands:
     - commands/autocomplete*.md
     - commands/*.md