docs(install): add Grok Build marketplace install path

Strangers use: grok plugin marketplace add 88plug/claude-code-plugins
then grok plugin install <name>@88plug --trust (alongside Claude /plugin).

Author: 88plug

README.md

@@ -20,6 +20,14 @@ Discover, catalog, and rank everything you've built or sketched on a machine —
 /plugin install project-prospector@88plug
 ```
 
+### Grok Build
+
+```text
+grok plugin marketplace add 88plug/claude-code-plugins
+grok plugin install project-prospector@88plug --trust
+```
+
+
 ## Quickstart
 
 Ask in plain language — no command to memorize:

docs/index.md

@@ -17,6 +17,14 @@ idea-novelty and leverage.
 /plugin install project-prospector@88plug
 ```
 
+### Grok Build
+
+```text
+grok plugin marketplace add 88plug/claude-code-plugins
+grok plugin install project-prospector@88plug --trust
+```
+
+
 Local clone (for development):
 
 ```text