docs: improve contributing doc, add GitHub PR template

Author: Fizzadar

.github/PULL_REQUEST_TEMPLATE.md

@@ -0,0 +1,15 @@
+<!--
+    🎉 Thank you for taking the time to contribute to pyinfra! 🎉
+
+    Please provide a short description of the proposed change and here's a handy checklist of things
+    to make PRs quicker to review and merge.
+
+    Note that we will not merge new connectors, but instead welcome PRs that link to thid party
+    connector packages.
+-->
+
+- [ ] Pull request is based on the default branch (`3.x` at this time)
+- [ ] Pull request includes tests for any new/updated operations/facts
+- [ ] Pull request includes documentation for any new/updated operations/facts
+- [ ] Tests pass (see `scripts/dev-test.sh`)
+- [ ] Type checking & code style passes (see `scripts/dev-lint.sh`)

docs/contributing.md

@@ -8,8 +8,8 @@ Third party pull requests help expand pyinfra's functionality and are essential
 
 + [How to write operations](api/operations)
 + [How to write facts](api/facts)
-+ [How to write connectors](api/connectors)
-+ [API reference](api/reference)
++ [How to write connectors](api/connectors) - note that new connectors **will not be merged to pyinfra**, instead they should be provided as a separate installable package. PR's that link to these packages in the docs very welcome.
++ Low level [API reference](api/reference) - this is pyinfra's internal APIs and does not come with the same compatibility guarantees as facts & operations - ie expect breaking changes on non-major versions.
 
 ## Branches
 
@@ -38,6 +38,10 @@ Code style is enforced via Black, isort and flake8. Types are checked with mypy
 scripts/dev-lint.sh
 ```
 
+### Commit Messages
+
+Please try to use consistent commit messages, look at the [recent history](https://github.com/pyinfra-dev/pyinfra/commits/) for examples. PRs that follow this will be rebased, PRs that do not will be squashed.
+
 ### Tests
 
 GitHub will run all the test suites as part of any pull requests. There's a handy script that runs the unit tests: