docs(other-hosts): add Pi install entry

Pi implements the Agent Skills standard natively and discovers skills from
~/.agents/skills/ and .agents/skills/ with no plugin or config file, so its
package manager installs the pack directly from git.

Follows the Adding a Host Guide bar (CONTRIBUTING.md): one line, host name
and install command only.

Refs #355, #365

docs/other-hosts.md

@@ -5,3 +5,4 @@ These hosts install the pack but are not in the README's install section, becaus
 Skills are plain `SKILL.md` folders, so any agent that reads the Agent Skills layout can load them. See [getting-started.md](getting-started.md).
 
 - **Oh My Pi**: `omp plugin marketplace add addyosmani/agent-skills`, then `omp plugin install agent-skills@addy-agent-skills`
+- **Pi**: `pi install git:github.com/addyosmani/agent-skills`