fix: add example historical version (#150)

## Description
- adds example historical version to doc

## User Facing
- [x] Yes

---------

Co-authored-by: Derek Lee <103802618+leeederek@users.noreply.github.com>

docs/docs/guides/installing-historical-versions.md

@@ -26,8 +26,8 @@ If you're looking to install the latest version of Kurtosis, [see here][install-
  ```
  brew uninstall kurtosis-tech/tap/kurtosis-cli
  ```
-
-2. Install an earlier version of Kurtosis
+ 
+2. Install an earlier version of Kurtosis (eg. `0.68.6`)
  ```
  brew install kurtosis-tech/tap/kurtosis-cli@<version>
  ```