Update README install command for official marketplace (#23)

* Update README install command for official marketplace

Now that the plugin is in the Anthropic Plugin Marketplace
(claude-plugins-official), use the simpler install command.

* Add alternative repo-based install command

* Improve install section wording

Author: mraible

README.md

@@ -18,17 +18,17 @@ AI coding assistant skills for building [CrowdStrike Falcon Foundry](https://www
 
 ### Claude Code (Tested)
 
-Install as a plugin from the [Anthropic Plugin Marketplace](https://github.com/anthropics/claude-plugins-official):
+Install from the [Anthropic Plugin Marketplace](https://github.com/anthropics/claude-plugins-official):
 
 ```
-/plugin install CrowdStrike/foundry-skills
+/plugin install crowdstrike-falcon-foundry
 ```
 
 Or register this repo as a plugin marketplace, then install:
 
 ```
 /plugin marketplace add CrowdStrike/foundry-skills
-/plugin install crowdstrike-falcon-foundry@foundry-skills
+/plugin install crowdstrike-falcon-foundry@foundry-marketplace
 ```
 
 Or install from a local clone for development: