[CRIU] [PATCH] README: contrinuting: add request to avoid force-push to an existing PR

[Mike Rapoport]

The updates of an existing pull request are hard to review because it is
not clear what was changed from the previous version.
It would be easier for reviewers and maintainers to have the PR closed
and then opened again with the updated changes and a brief description
of changes between the versions.

Add a text to README.md that will emphasize this.

Signed-off-by: Mike Rapoport <rppt at linux.ibm.com>
---
 README.md | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/README.md b/README.md
index 6a578b953..6f82c8241 100644
--- a/README.md
+++ b/README.md
@@ -68,6 +68,8 @@ Here are some useful hints to get involved.
 * Documentation is always hard, we have [some information](https://criu.org/Category:Empty_articles) that is to be extracted from people's heads into wiki pages as well as [some texts](https://criu.org/Category:Editor_help_needed) that all need to be converted into useful articles;
 * Feedback is expected on the github issues page and on the [mailing list](https://lists.openvz.org/mailman/listinfo/criu);
 * We accept github pull requests and this is the preferred way to contribute to CRIU. If you prefer to send patches by email, you are welcome to send them to [the devel list](http://criu.org/How_to_submit_patches);
+  * Please avoid force pushing updates to an existent pull request. Close the pull request and open a new one with the updated changes.
+  * Mention what were the changes between different versions of a pull request. It makes reviewers and maintainers life much easier.
 * Spread the word about CRIU in [social networks](http://criu.org/Contacts);
 * If you're giving a talk about CRIU -- let us know, we'll mention it on the [wiki main page](https://criu.org/News/events);
 
-- 
2.25.4