chore: update manual backport readme and trop comment with e backport command

docs/manual-backports.md

@@ -1,6 +1,6 @@
 # Manual Backports
 
-When `trop` fails to backport your PR (trust us it tried its best) you need to backport the PR manually. You can do this by cherry-picking the commits in the PR yourself locally and pushing up a new branch.
+When `trop` fails to backport your PR (trust us it tried its best) you need to backport the PR manually. You can do this by cherry-picking the commits in the PR yourself locally and pushing up a new branch or using a [`build-tools` command](#build-tools-backport-command).
 
 When you create PR for a manual backport, the body of the backport PR must contain: 
 
@@ -23,6 +23,10 @@ Backport of https://github.com/electron/electron/pull/21813
 If you raise a PR to a branch that isn't `main` or a release branch without including a valid reference as above, `trop` will create a
 "failed" check on that PR to prevent it being merged.
 
+## Build Tools Backport Command
+
+You can use the `e backport <PR>` command to backport PRs. [This command](https://github.com/electron/build-tools?tab=readme-ov-file#e-backport-pr) manually backports PRs by automating the steps above.
+
 ## Skipping Backport Checks
 
 Sometimes development flows will necessitate a PR train, or several linked PRs to be merged into one another successively where none is a backport. To account for this case, `trop` allows for a label to be set on the non-backport PR: `SKIP_CHECK_LABEL`.

src/utils.ts

@@ -726,7 +726,7 @@ export const backportImpl = async (
           context.repo({
             issue_number: pr.number,
             body: `I was unable to backport this PR to "${targetBranch}" cleanly;
-   you will need to perform this backport manually.`,
+   you will need to perform this [backport manually](https://github.com/electron/trop/blob/main/docs/manual-backports.md#manual-backports).`,
           }),
         );