[#183] Unlink API.md to README file

This is useful for auto-generated document tools
which parse docs dir.

Signed-off-by: Alex Vanin <a.vanin@yadro.com>

docs/api.md

@@ -8,7 +8,7 @@
 | `/zip/{cid}/{prefix}`                           | [Download objects in archive](#download-zip) |
 
 **Note:** `cid` parameter can be base58 encoded container ID or container name
-(the name must be registered in NNS, see appropriate section in [README](../README.md#nns)).
+(the name must be registered in NNS, see appropriate section in [nns.md](./nns.md)).
 
 Route parameters can be:
 
@@ -18,7 +18,7 @@ Route parameters can be:
 
 ### Bearer token
 
-All routes can accept [bearer token](../README.md#authentication) from:
+All routes can accept [bearer token](./authentication.md) from:
 
 * `Authorization` header with `Bearer` type and base64-encoded token in
   credentials field