docs: add pnpm to list of install options

Author: VividLemon

apps/docs/docs/getting-started/README.md

@@ -57,6 +57,14 @@ yarn add bootstrap bootstrap-vue-3
 
 ```bash
 npm install bootstrap bootstrap-vue-3
+```
+
+  </CodeGroupItem>
+
+  <CodeGroupItem title="PNPM">
+
+```bash
+pnpm add bootstrap bootstrap-vue-3
 ```
 
   </CodeGroupItem>
@@ -99,6 +107,14 @@ yarn add bootstrap bootstrap-vue-3
 
 ```bash
 npm install bootstrap bootstrap-vue-3
+```
+
+  </CodeGroupItem>
+
+  <CodeGroupItem title="PNPM">
+
+```bash
+pnpm add bootstrap bootstrap-vue-3
 ```
 
   </CodeGroupItem>