doc: add a doc to explain how to connect to a skill by http-based url or a .zip file

docs/addskill.md

@@ -0,0 +1,33 @@
+# How to connect to a skill
+
+In Bot framework composer, you can "connect to a skill" by providing a http-based manifest URL or a local compressed (.zip) file.
+
+- The http-based manifest URL should be accessible and a valid manifest JSON file. Otherwise, "connect to a skill" will be failed.
+- The local compressed file should include one and only one valid manifest JSON file and corresponding language file if needed.
+
+For manifest version, Composer support manifest v2.0, v2.1 and v2.2.
+- Manifest v2.0.
+- Manifest v2.1 - support dispatch modal.
+- Manifest v2.2 - support uri-reference in privacyUrl, iconUrl and language dispatch modal.
+
+Examples:
+1. A http-based manifest url.
+```
+  https://github.com/microsoft/botframework-sdk/blob/main/schemas/skills/v2.1/samples/complex-skillmanifest.json
+```
+
+2. A .zip file usually contains 
+- (required) a manifest json. (User will get an error if no manifest or multiple manifests found in the zip)
+- (optional) dispatch models. (.lu or .qna files)
+- (optional) privacy file. 
+- (optional) icon file. 
+
+If the manifest.json is v2.2, dispatch models, privacy file and icon file can all be a relative path in the manifest.json.
+
+See more details in the following example. 
+```
+  https://github.com/microsoft/botframework-sdk/tree/main/schemas/skills/v2.2/samples/relativeUris
+```
+
+
+