docs: touch up package init docs (#1605)

## Description:
This PR cleans up the package init docs:
- adds sidebar label
- change title
- re-word some words

## Is this change user facing?
YES
<!-- If yes, please add the "user facing" label to the PR -->
<!-- If yes, don't forget to include docs changes where relevant -->

## References (if applicable):
#1547

---------

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

docs/docs/cli-reference/package-init.md

@@ -1,14 +1,19 @@
-# kurtosis package init
-This command initializes the current directory to be a [Kurtosis package][package] by creating a [`kurtosis.yml` file][kurtosis-yml] with the given package name.
+---
+title: package init
+sidebar_label: package init
+slug: /package-init
+---
+
+The `package init` command converts the current directory into a [Kurtosis package][package] by generating a new [`kurtosis.yml`][kurtosis-yml] file and a `main.star` file using the given package name, if they do not already exist.
 
 ```
-Usage:
-  kurtosis package init [flags] package_name
+kurtosis package init $PACKAGE_NAME
 ```
 
-The `package_name` argument is the [locator][locators]to the package, in the format `github.com/USER/REPO`.
+The optional `$PACKAGE_NAME` argument is the [locator][locators] to the package, in the format `github.com/USER/REPO`. If an argument is not passed, the package locator will simply be: `github.com/example-org/example-package` by default.
 
+<!---------------------->
 [package]: ../concepts-reference/packages.md
 [kurtosis-yml]: ../concepts-reference/kurtosis-yml.md
 [locators]: ../concepts-reference/locators.md
-[executable-package]: ../concepts-reference/packages.md#runnable-packages
+[executable-package]: ../concepts-reference/packages.md#runnable-packages