docs: [FUN-564] Add link to ref docs in Dev server README (#506)

* Add link to ref docs in Dev server README

* move into main readme

* newline

* copy blurb from ref docs

* remove extra whitespace

* migrate text, pare down words

Author: tvarney13

README.md

@@ -95,6 +95,7 @@ Running this command creates a configuration file located at `$XDG_CONFIG_HOME/l
 LaunchDarkly CLI commands:
 
 - `setup` guides you through creating your first flag, connecting an SDK, and evaluating your flag in your Test environment
+- `dev-server` lets you start a local server and retrieve flag values from a LaunchDarkly source environment so you can test your code locally. For assistance starting with or running dev-server, refer to the [reference docs](https://launchdarkly.com/docs/guides/flags/ldcli-dev-server).
 
 ### Resource Commands