Set add -p as beta (#1140)

tools/apis/cds-add.md

@@ -303,6 +303,26 @@ module.exports = class extends cds.add.Plugin {
 ```
 :::
 
+#### Call `cds add` for an NPM package <beta />
+
+Similar to `npx -p`, you can use the `--package/-p` option to directly install a package from an *npm* registry before running the command.
+This lets you invoke `cds add` for CDS plugins easily with a single command:
+
+```sh
+cds add my-facet -p @cap-js-community/example
+```
+
+::: details Install directly from your GitHub branch
+
+ For example, if your plugin's code is in `https://github.com/cap-js-community/example` on branch `cds-add` and registers the  command `cds add my-facet`, then doing an integration test of your plugin with `@sap/cds-dk` in a single command:
+
+```sh
+cds add my-facet -p @cap-js-community/example@git+https://github.com/cap-js-community/example#cds-add
+```
+
+:::
+
+
 ## Plugin API
 
 Find here a complete overview of public `cds add` APIs.