docs(skill): clarify AgentSkills vs. clone-based execution

Add a "Getting the executable scripts" section to the root SKILL.md.
`npx skills add aloth/PowerSkills` only publishes the Markdown skill
definitions into ~\.agents\skills\powerskills\; the .ps1 scripts that
actually do the work are not copied there, which surprised early users.

The new section:

- Explains what AgentSkills installs vs. what it does not.
- Shows the `git clone` command to get a working copy.
- Documents the recommended
  `powershell -NoProfile -ExecutionPolicy Bypass -File ...` invocation.
- Recommends storing the path once (either agent-side or as a
  POWERSKILLS_ROOT environment variable) to avoid hard-coding it in
  every skill call.

Author: aloth

SKILL.md

@@ -17,6 +17,30 @@ Windows capabilities for AI agents via PowerShell. Each skill in `skills/` is in
 Set-ExecutionPolicy -Scope CurrentUser -ExecutionPolicy RemoteSigned
 ```
 
+## Getting the executable scripts
+
+AgentSkills (`npx skills add aloth/PowerSkills`) only publishes the Markdown skill definitions into `~\.agents\skills\powerskills\` (and the per-skill sub-folders). The `.ps1` files that actually do the work are **not** copied there. To run any action you need a working copy of this repository on disk:
+
+```powershell
+# Clone once, anywhere you like
+git clone https://github.com/aloth/PowerSkills.git C:\Tools\PowerSkills
+```
+
+Invoke the CLI with the full path to `powerskills.ps1`:
+
+```powershell
+powershell -NoProfile -ExecutionPolicy Bypass `
+  -File C:\Tools\PowerSkills\powerskills.ps1 <skill> <action> [--param value ...]
+```
+
+To avoid repeating the path, either store it agent-side once or set an env var and reference that from any shell:
+
+```powershell
+[Environment]::SetEnvironmentVariable("POWERSKILLS_ROOT", "C:\Tools\PowerSkills", "User")
+# New shells then use:
+powershell -NoProfile -ExecutionPolicy Bypass -File "$env:POWERSKILLS_ROOT\powerskills.ps1" list
+```
+
 ## Usage
 
 ```powershell