add instructions on how to setup command completion for awslocal (#55)

* add instructions on how to setup command completion for awslocal

* Update README.md

Co-authored-by: Harsh Mishra <erbeusgriffincasper@gmail.com>

Author: alexrashed

README.md

@@ -22,8 +22,7 @@ pip install awscli-local
 
 ## Usage
 
-The `awslocal` command has the same usage as the `aws` command. For detailed usage,
-please refer to the man pages of `aws help`.
+The `awslocal` command has the same usage as the `aws` command. For detailed usage, please refer to the manual pages of `aws help`.
 
 ## Example
 
@@ -49,13 +48,44 @@ localstack is bound to another interface (i.e. docker-machine).
 with `USE_SSL=true` enabled). Defaults to `false`.
 * `DEFAULT_REGION`: Set the default region. Overrides `AWS_DEFAULT_REGION` environment variable.
 
+## Completion
+
+`awscli` provides a neat command completion feature which is compatible with most modern shells which can also be used with `awslocal`.
+
+### Usage instructions
+
+The command completion will automatically suggest commands and parameters when using the completion key (which is typically the _Tab_ key):
+
+```sh
+$ awslocal dynamodb d<TAB>
+delete-backup                        describe-global-table
+delete-item                          describe-global-table-settings
+delete-table                         describe-limits
+describe-backup                      describe-table
+describe-continuous-backups          describe-table-replica-auto-scaling
+describe-contributor-insights        describe-time-to-live
+describe-endpoints
+```
+
+### Configuration
+
+- Follow the official guide on setting up the command completion for the `aws` CLI: https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-completion.html
+- While enabling the command completion for your shell, **make sure to register the completion for `awslocal` as well**.
+
+  For example, if you are using `bash`, you would add the following commands to your `~/.bashrc`:
+  ```sh
+  complete -C '/usr/local/bin/aws_completer' aws
+  complete -C '/usr/local/bin/aws_completer' awslocal
+  ```
+- Follow the instructions for the shell you are using. For some shells you might need to register a different command or enable certain compatibility plugins (like `zsh`).
+
 ## Limitations
 
 * Please note that there is a known limitation for using the `cloudformation package ...` command with the AWS CLI v2. The problem is that the AWS CLI v2 is [not available as a package on pypi.org](https://github.com/aws/aws-cli/issues/4947), but is instead shipped as a binary package that cannot be easily patched from `awslocal`. To work around this issue, you have 2 options:
 
    - Downgrade to the v1 AWS CLI (this is the recommended approach)
    - There is an inofficial way to install AWS CLI v2 from sources. We do not recommend this, but it is technically possible. Also, you should install these libraries in a Python virtualenv, to avoid version clashes with other libraries on your system:
-```console
+```sh
 virtualenv .venv
 . .venv/bin/activate
 pip install https://github.com/boto/botocore/archive/v2.zip https://github.com/aws/aws-cli/archive/v2.zip