Describe linked issues can use trailer syntax (github#36607)

Co-authored-by: Ben Ahmady <[email protected]>

Author: lumynou5

content/issues/tracking-your-work-with-issues/using-issues/linking-a-pull-request-to-an-issue.md

@@ -54,6 +54,8 @@ Issue in the same repository | KEYWORD #ISSUE-NUMBER | `Closes #10`
 Issue in a different repository | KEYWORD OWNER/REPOSITORY#ISSUE-NUMBER | `Fixes octo-org/octo-repo#100`
 Multiple issues | Use full syntax for each issue | `Resolves #10, resolves #123, resolves octo-org/octo-repo#100`
 
+The keywords can be followed by colons or in uppercase. For example: `Closes: #10`, `CLOSES #10`, or `CLOSES: #10`.
+
 Only manually linked pull requests can be manually unlinked. To unlink an issue that you linked using a keyword, you must edit the pull request description to remove the keyword.
 
 You can also use closing keywords in a commit message. The issue will be closed when you merge the commit into the default branch, but the pull request that contains the commit will not be listed as a linked pull request.