clarify that (if) small PRs can be submitted without issues first

- To meet JOSS requirements of 'clear instructions for contributing' openjournals/joss-reviews#4405, instructions in the two sections need to be consistent
- Currently the Pull Request Process section allows small PRs without an issue but the Contributing section does not
- sometimes (like now) it is easier to create the PR and have it serve the function of the issue, so this PR proposes update in that direction!

CONTRIBUTING.md

@@ -1,6 +1,6 @@
 # Contributing
 
-When contributing to this project, please first discuss the change you wish to make via [issue](https://github.com/agrdatasci/climatrends/issues) before making a change and pull request. Please submit questions, bug reports, and requests in the issues tracker.
+When contributing to this project, please first discuss the change you wish to make via [issue](https://github.com/agrdatasci/climatrends/issues) before making a change and pull request, unless it is a minor change that doesn't affect package functionality. Please submit questions, bug reports, and requests in the issues tracker.
 
 Note that we have a [code of conduct](https://agrdatasci.github.io/climatrends/CODE_OF_CONDUCT.html), please follow it in all your interactions with the project.
 
@@ -12,4 +12,4 @@ If you plan to contribute, please read our pull request process.
 2. If you have large changes, please open an [issue](https://github.com/agrdatasci/climatrends/issues) first to discuss.
 3. Documentation is generated by [roxygen2](https://CRAN.R-project.org/package=roxygen2). Please write documentation in code files and let it auto-generate documentation files. We use a recent version and write the documentation in markdown. The [R Packages](https://r-pkgs.org/) book by Hadley Wickham and Jennifer Bryan may help you. 
 4. Write and test your code with [goodpractice](https://CRAN.R-project.org/package=goodpractice) before submitting your change.
-5. Push to the origin repository.
+5. Push to the origin repository.