Improve Pull Request guidelines

- Splits PR advice into two sections.
- Add "co-authored-by" instructions.
- Add description of draft PR and when using it is appropriate.
- Reword ZFS Test Suite checklist question.
- Link to zfs-tests.sh and zloop.sh.

Reviewed-By: Marcel Schilling <marcel.schilling@mdc-berlin.de>
Reviewed-By: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-By: Richard Laager <rlaager@wiktel.com>
Co-Authored-By: Marcel Schilling <marcel.schilling@mdc-berlin.de>
Co-Authored-By: Brian Behlendorf <behlendorf1@llnl.gov>
Co-Authored-By: Richard Laager <rlaager@wiktel.com>
Signed-off-by: Kjeld Schouten-Lebbing <kjeld@schouten-lebbing.nl>
Closes #9753

.github/CONTRIBUTING.md

@@ -120,6 +120,9 @@ Otherwise, open a new issue and describe your proposed feature.  Why is this
 feature needed?  What problem does it solve?
 
 ### Pull Requests
+
+#### General
+
 * All pull requests must be based on the current master branch and apply
 without conflicts.
 * Please attempt to limit pull requests to a single commit which resolves
@@ -133,7 +136,20 @@ logically independent patches which build on each other.  This makes large
 changes easier to review and approve which speeds up the merging process.
 * Try to keep pull requests simple. Simple code with comments is much easier
 to review and approve.
+* All proposed changes must be approved by a ZFS on Linux organization member.
+* If you have an idea you'd like to discuss or which requires additional testing, consider opening it as a draft pull request. 
+Once everything is in good shape and the details have been worked out you can remove its draft status. 
+Any required reviews can then be finalized and the pull request merged.
+
+#### Tests and Benchmarks
+* Every pull request will by tested by the buildbot on multiple platforms by running the [zfs-tests.sh and zloop.sh](
+https://github.com/zfsonlinux/zfs/wiki/Building-ZFS#running-zloopsh-and-zfs-testssh) test suites.
+* To verify your changes conform to the [style guidelines](
+https://github.com/zfsonlinux/zfs/blob/master/.github/CONTRIBUTING.md#style-guides
+), please run `make checkstyle` and resolve any warnings.
+* Static code analysis of each pull request is performed by the buildbot; run `make lint` to check your changes.
 * Test cases should be provided when appropriate.
+This includes making sure new features have adequate code coverage.
 * If your pull request improves performance, please include some benchmarks.
 * The pull request must pass all required [ZFS
 Buildbot](http://build.zfsonlinux.org/) builders before
@@ -142,7 +158,6 @@ builder failures, you may be experiencing a [test suite
 issue](https://github.com/zfsonlinux/zfs/issues?q=is%3Aissue+is%3Aopen+label%3A%22Test+Suite%22).
 There are also various [buildbot options](https://github.com/zfsonlinux/zfs/wiki/Buildbot-Options)
 to control how changes are tested.
-* All proposed changes must be approved by a ZFS on Linux organization member.
 
 ### Testing
 All help is appreciated! If you're in a position to run the latest code
@@ -290,3 +305,14 @@ Git can append the `Signed-off-by` line to your commit messages. Simply
 provide the `-s` or `--signoff` option when performing a `git commit`.
 For more information about writing commit messages, visit [How to Write
 a Git Commit Message](https://chris.beams.io/posts/git-commit/).
+
+#### Co-authored By
+If someone else had part in your pull request, please add the following to the commit:
+`Co-authored-by: Name <gitregistered@email.address>`
+This is useful if their authorship was lost during squashing, rebasing, etc.,
+but may be used in any situation where there are co-authors.
+
+The email address used here should be the same as on the GitHub profile of said user.
+If said user does not have their email address public, please use the following instead:
+`Co-authored-by: Name <[username]@users.noreply.github.com>`
+

.github/PULL_REQUEST_TEMPLATE.md

@@ -19,6 +19,7 @@ https://github.com/zfsonlinux/zfs/wiki/Buildbot-Options
 <!--- Include details of your testing environment, and the tests you ran to -->
 <!--- see how your change affects other areas of the code, etc. -->
 <!--- If your change is a performance enhancement, please provide benchmarks here. -->
+<!--- Please think about using the draft PR feature if appropriate -->
 
 ### Types of changes
 <!--- What types of changes does your code introduce? Put an `x` in all the boxes that apply: -->
@@ -36,5 +37,5 @@ https://github.com/zfsonlinux/zfs/wiki/Buildbot-Options
 - [ ] I have updated the documentation accordingly.
 - [ ] I have read the [**contributing** document](https://github.com/zfsonlinux/zfs/blob/master/.github/CONTRIBUTING.md).
 - [ ] I have added [tests](https://github.com/zfsonlinux/zfs/tree/master/tests) to cover my changes.
-- [ ] All new and existing tests passed.
+- [ ] I have run the ZFS Test Suite with this change applied.
 - [ ] All commit messages are properly formatted and contain [`Signed-off-by`](https://github.com/zfsonlinux/zfs/blob/master/.github/CONTRIBUTING.md#signed-off-by).