Add 'RPC failed' error handling while fetching from gitee.com

Added information which describes how to change http and https postBuffer, which solves fetching from gitee.com problems which may occur during the build.

Closes https://gitlab.eclipse.org/eclipse/oniro-core/meta-openharmony/-/issues/36

Signed-off-by: Grzegorz Gwóźdź grzegorz.gwozdz@huawei.com

recipes-openharmony/images/README.md

 <!--
 SPDX-FileCopyrightText: Huawei Inc.
 
 SPDX-License-Identifier: CC-BY-4.0
@@ -17,4+17,4 @@
 
     bitbake openharmony-standard-image
 
-To run it, run the this commands after successfully completing the above build command:
+
+You may encounter error `RPC failed` during fetching files from gitee.com. In order to fix it, run following commands:
+
+    git config --global http.postBuffer 1048576000
+    git config --global https.postBuffer 1048576000
+    
+and rebuild the image.
+
+To run the image, run this command after successfully completing the above build command:
 
     runqemu serialstdio nographic slirp