Add basic CLI docs

Author: axelrindle

docs/docs/cli/01-installation.md

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+# Installation
+
+## npm
+
+```shell
+npm install -g @github-version-checker/cli
+```
+
+## Binary
+
+Download a binary version from the [releases page](https://github.com/axelrindle/github-version-checker/releases).

docs/docs/cli/02-examples.md

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+# Usage Examples
+
+## Basic
+
+```shell
+$ github-version-checker \
+    --owner axelrindle \
+    --repository github-version-checker \
+    --current-version 2.2.0
+```
+
+```
+An update is available! v3.0.0
+You are on version 2.3.0!
+```
+
+## With json output
+
+```shell
+$ github-version-checker --json \
+    --owner axelrindle \
+    --repository github-version-checker \
+    --current-version 2.2.0
+```
+
+```json
+{
+  "type": "outdated",
+  "data": {
+    "name": "v2.3.0",
+    "tag": {
+      "name": "2.3.0"
+    },
+    "isPrerelease": false,
+    "isDraft": false,
+    "publishedAt": "2022-03-18T15:22:03Z",
+    "url": "https://github.com/axelrindle/github-version-checker/releases/tag/2.3.0"
+  }
+}
+```

docs/docs/cli/_category_.json

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+{
+    "label": "⌨️ Command Line Interface (CLI)",
+    "position": 5,
+    "link": {
+        "type": "doc",
+        "id": "cli/index"
+    }
+}

docs/docs/cli/index.md

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+# Command Line Interface (CLI)
+
+The CLI is planned to be releases with v3.0.0 and offers to perform a version check in non Node.js environments. It supports
+plain-text and JSON-formatted output.
+
+## Usage
+
+```
+
+  $ github-version-checker [options]
+
+  Options
+    -o, --owner              The repository owner. May be a username or organization name.
+    -r, --repository         The repository name.
+    -c, --current-version    The current application version.
+    -t, --tags               Fetches tags instead of releases.
+    --no-pre-releases        Excludes pre-releases.  (default false)
+    --token                  A PAT to use.
+    --json                   Outputs the raw result data as JSON.  (default false)
+    --verbose                Enables verbose logging.  (default false)
+    -v, --version            Displays current version
+    -h, --help               Displays this message
+
+```