docs: document pre-filling issues and pull requests from query parameters (#592)

Describe the query parameters of the new issue and pull request pages, including those added in https://github.com/go-gitea/gitea/pull/39804.

---------

Co-authored-by: Jakub Vrana <[email protected]>
Reviewed-on: https://gitea.com/gitea/docs/pulls/592
Reviewed-by: wxiaoguang <[email protected]>
Reviewed-by: bircni <[email protected]>
Co-authored-by: Jakub Vrána <[email protected]>

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

@@ -15,7 +15,7 @@ creating issues and pull requests. This will cut down on the initial back and fo
 of getting some clarifying details.
 It is currently not possible to provide generic issue/pull-request templates globally.
 
-Additionally, the New Issue page URL can be suffixed with `?title=Issue+Title&body=Issue+Text` and the form will be populated with those strings. Those strings will be used instead of the template if there is one.
+Additionally, the New Issue page URL can be suffixed with `?title=Issue+Title&body=Issue+Text` and the form will be populated with those strings. Those strings will be used instead of the template if there is one. See [Pre-filling Issues and Pull Requests](prefill-issues-pull-requests.md) for all parameters.
 
 ## File names
 

docs/usage/issues-prs/prefill-issues-pull-requests.md

@@ -0,0 +1,42 @@
+---
+date: "2026-10-17T00:00:00+00:00"
+slug: "prefill-issues-pull-requests"
+sidebar_position: 14
+---
+
+# Pre-filling Issues and Pull Requests
+
+Links to the pages for creating issues and pull requests can pre-fill the form with query parameters.
+This lets you link users from another app, a README or a project board to a form that is already categorized.
+
+- New issue: `/{owner}/{repo}/issues/new?…`
+- New pull request: `/{owner}/{repo}/compare/{base}...{head}?…`
+
+For example, this link opens a new issue with a title, two labels and an assignee:
+
+```
+https://gitea.example.com/owner/repo/issues/new?title=Dashboard+crashes&label=kind/bug,area/dashboard&assignee=alice
+```
+
+## Parameters
+
+| Parameter     | Value                                                                       |
+| ------------- | --------------------------------------------------------------------------- |
+| `title`       | Title                                                                       |
+| `body`        | Description                                                                 |
+| `label`       | Comma-separated label IDs or names                                          |
+| `labels`      | Alias of `label`                                                            |
+| `milestone`   | Milestone ID or name                                                        |
+| `project`     | Comma-separated project IDs or titles                                       |
+| `assignee`    | Comma-separated user IDs or usernames                                       |
+| `template`    | File name of the [template](issue-pull-request-templates.md) to use         |
+| `field:<id>`  | Value of the field with this `id` in a YAML template                        |
+
+IDs and names can be mixed and names are matched case-insensitively. Values that don't match anything in the repository are ignored.
+Labels include the organization's labels, and closed milestones and projects can be selected too.
+Milestones and projects are only offered to users who can write to issues or pull requests, so for other users these parameters have no effect.
+
+The values from the link take precedence over the title, description, labels and assignees of the template.
+
+When there are several issue templates to choose from, the parameters are passed through to the chosen one.
+On the compare page, any of these parameters also opens the pull request form directly, as `expand=1` does.