Add usage docs for provider hub (#97)

* Add usage docs for provider hub

Co-authored-by: Ron <[email protected]>

docs/index.md

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+## AWS Provider
+
+The CloudQuery AWS provider pulls configuration out of AWS resources, normalizes them and stores them in PostgreSQL database.
+
+### Install
+
+```shell
+cloudquery init aws
+```
+
+### Authentication
+
+To authenticate cloudquery with your AWS account you can use any of the following options (see full documentation at [AWS SDK V2](https://aws.github.io/aws-sdk-go-v2/docs/configuring-sdk/#specifying-credentials)):
+
+- Static Credentials: `AWS_ACCESS_KEY_ID`, `AWS_SECRET_ACCESS_KEY`, `AWS_SESSION_TOKEN`
+- Shared configuration files (via `aws configure`).
+  - SDK defaults to `credentials` file under `.aws` folder that is placed in the home folder on your computer.
+  - SDK defaults to `config` file under `.aws` folder that is placed in the home folder on your computer.
+- If your application uses an ECS task definition or RunTask API operation, IAM role for tasks.
+- If your application is running on an Amazon EC2 instance, IAM role for Amazon EC2.
+
+### Configuration
+
+The following configuration section can be automaticlly generated by `cloudquery init aws`:
+
+```hcl
+provider "aws" {
+  configuration {
+    // Optional. if you want to assume role to multiple account and fetch data from them
+    //accounts "<YOUR ID>" {
+    // Optional. Role ARN we want to assume when accessing this account
+    // role_arn = <YOUR_ROLE_ARN>
+    // }
+    // Optional. by default assumes all regions
+    // regions = ["us-east-1", "us-west-2"]
+    // Optional. Enable AWS SDK debug logging.
+    aws_debug = false
+    // The maximum number of times that a request will be retried for failures. Defaults to 5 retry attempts.
+    // max_retries = 5
+    // The maximum back off delay between attempts. The backoff delays exponentially with a jitter based on the number of attempts. Defaults to 60 seconds.
+    // max_backoff = 30
+  }
+```
+
+By default cloudquery will fetch all configuration from **all** resources in **all** regions in the **default** account. You can change this behaviour with the following arguments:
+
+- `accounts` **(Optional)** - Specify multiple accounts to fetch data from them concurrently and then query across accounts. The default configured account should be able [AssumeRole](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRole.html) to the specified accounts.
+- `regions` **(Optional)** - limit fetching to specific regions.
+
+### Query Examples
+
+#### Find all public facing load balancers
+
+```sql
+SELECT * FROM aws_elbv2_load_balancers WHERE scheme = 'internet-facing';
+```
+
+#### Find all unencrypted RDS instances
+
+```sql
+SELECT * from aws_rds_clusters where storage_encrypted = 0;
+```
+
+#### Find all unencrypted buckets
+
+```sql
+SELECT * from aws_rds_clusters where storage_encrypted = 0;
+```