Added project config to issue template example (#428)

I have updated the docs since this feature is now supported.

Reviewed-on: https://gitea.com/gitea/docs/pulls/428
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: nico-i <nico@ismaili.de>
Co-committed-by: nico-i <nico@ismaili.de>

docs/usage/issues-prs/issue-pull-request-templates.md

@@ -100,6 +100,8 @@ about: "This template is for testing!"
 title: "[TEST] "
 ref: "main"
 assignees: ["user1"]
+projects:
+  - Example Project
 labels:
 
 - bug
@@ -114,6 +116,7 @@ In the above example, when a user is presented with the list of issues they can
 `This template is for testing!`. When submitting an issue with the above example, the issue title would be pre-populated with
 `[TEST] ` while the issue body would be pre-populated with `This is the template!`.
 The issue would be assigned to `user1`.
+The issue would be assigned to the project `Example Project`.
 The issue would also be assigned two labels,
 `bug` and `help needed`, and the issue will have a reference to `main`.