docs(readme): strip didactic noise from install section

Three trims:
- Dropped the agentskills.io link (community/third-party site, not
  Anthropic-official; risks looking like a placeholder reference).
- Removed the bullet explanations of what each /plugin command does
  and the /plugin UI alternative paragraph — the two commands are
  self-explanatory, the explanations were noise.
- Removed the 'why we use --path' note for Gemini and the 'after
  install' summary — the SKILL.md link covers what users need.

Result: 3 install snippets + one safety sentence, ~half the length.

Author: KylinMountain

README.md

@@ -238,47 +238,30 @@ OpenKB's wiki is a directory of Markdown files with `[[wikilinks]]`. Obsidian re
 
 ### Using with Claude Code / Codex / Gemini CLI
 
-OpenKB ships a [SKILL.md](https://agentskills.io/) so any agent CLI can read your compiled wiki — no extra runtime, no MCP setup, just install the skill once.
+OpenKB ships a `SKILL.md` so any agent CLI can read your compiled wiki — no extra runtime, no MCP setup, just install the skill once.
 
-#### Claude Code
-
-Two commands — first register OpenKB as a plugin marketplace, then install the skill from it:
+**Claude Code**:
 
 ```
 /plugin marketplace add VectifyAI/OpenKB
 /plugin install openkb@vectify
 ```
 
-- `/plugin marketplace add VectifyAI/OpenKB` reads `.claude-plugin/marketplace.json` from the repo's default branch and registers `vectify` as a known marketplace.
-- `/plugin install openkb@vectify` installs the `openkb` plugin from that marketplace. The `@vectify` suffix names the marketplace, not the package.
-
-Alternative — `/plugin` (interactive UI) lets you browse registered marketplaces and install with one click, but you still need to `marketplace add` first to register the source.
-
-To remove later: `/plugin uninstall openkb` then `/plugin marketplace remove VectifyAI/OpenKB`.
-
-#### Gemini CLI
-
-Native [skills installer](https://geminicli.com/docs/cli/skills/) fetches the skill folder from this repo. `--path skills/openkb` points it at the sub-directory containing `SKILL.md` (the rest of the repo is the openkb codebase, not skill content):
+**Gemini CLI**:
 
 ```bash
 gemini skills install https://github.com/VectifyAI/OpenKB.git --path skills/openkb --consent
 ```
 
-#### OpenAI Codex CLI
-
-Codex has no marketplace command yet — install by cloning the repo and symlinking the skill folder into one of its discovery paths:
+**OpenAI Codex CLI** (no marketplace command yet — manual symlink):
 
 ```bash
 git clone https://github.com/VectifyAI/OpenKB.git ~/openkb-src
 mkdir -p ~/.agents/skills
 ln -s ~/openkb-src/skills/openkb ~/.agents/skills/openkb
 ```
 
-Codex discovers skills under `.agents/skills/` walking up from cwd, or `~/.agents/skills/` for user-scope. To update later: `cd ~/openkb-src && git pull`.
-
-#### After install
-
-When you ask about content in an OpenKB knowledge base, the skill activates and points the agent at `openkb status` to discover the KB root, `openkb list` for the document catalog, and direct Markdown reads for concept and summary content. The skill is read-only: it won't run `openkb add`, `remove`, or `lint --fix` without you asking. See [`skills/openkb/SKILL.md`](skills/openkb/SKILL.md) for the full instruction set the agent receives.
+The skill is read-only — it won't run `openkb add`, `remove`, or `lint --fix` without you asking. See [`skills/openkb/SKILL.md`](skills/openkb/SKILL.md) for the full instruction set.
 
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