docs: update manifest-releaser docs to add some clarification around … (

#2331)

* docs: update manifest-releaser docs to add some clarification around the package path

- make it a little clearer that the package path should be a folder and not a file
- give an example for creating an empty release-please-manifest.json

Signed-off-by: Amo Chumber <amo@sysadmiral.xyz>

* Update manifest-releaser.md

---------

Signed-off-by: Amo Chumber <amo@sysadmiral.xyz>
Co-authored-by: Jeff Ching <chingor@google.com>

docs/manifest-releaser.md

@@ -47,7 +47,13 @@ Create a minimal `release-please-config.json`, e.g., for a single JS package:
 }
 ```
 
-Create an empty `.release-please-manifest.json`
+> Note: `path/to/pkg` should be a directory and not a file.
+
+Create an empty `.release-please-manifest.json`. For example:
+```shell
+echo "{}" > .release-please-manifest.json
+```
+
 
 Commit/push/merge these to your remote GitHub repo (using either the repo's
 default branch or a test branch in which case you'll use the `--target-branch`
@@ -269,7 +275,7 @@ defaults (those are documented in comments)
       "exclude-paths": ["path/to/myPyPkgA"]
     },
 
-    // path segment should be relative to repository root
+    // path segment should be a folder relative to repository root
     "path/to/myJSPkgA": {
       // overrides release-type for node
       "release-type": "node",