Add pull-request best practices guide (#70)

# Description

Adds pull request best practices to CONTRIBUTING.md and references this
document + pull request best practices in the pull_request_template.md
so all contributors are confronted with this guide before they open a
pull request rather than afterward by the bot.

Co-authored-by: Michael Kubacki <[email protected]>
Co-authored-by: Erich-McMillan <[email protected]>

Author: 3 people

.sync/github_templates/contributing/CONTRIBUTING.md

@@ -46,6 +46,52 @@ If you cannot find an existing issue that describes your bug or feature, create
 Please continue to follow your request after it is submitted to assist with any additional information that might be
 requested.
 
+### Pull Request Best Practices
+
+Pull requests for UEFI code can become large and difficult to review due to the large number of build and
+configuration files. To aid maintainers in reviewing your code, we suggest adhering to the following guidelines:
+
+1. Do keep code reviews single purpose; don't add more than one feature at a time.
+2. Do fix bugs independently of adding features.
+3. Do provide documentation and unit tests.
+4. Do introduce code in digestible amounts.
+   * If the contribution logically be broken up into separate pull requests that independently build and function
+     successfully, do use multiple pull requests.
+
+#### Code Categories
+
+To keep code digestible, you may consider breaking large pull requests into three categories of commits within the pull
+request.
+
+1. **Interfaces**: .h, .inf, .dec, documentation
+2. **Implementation**: .c, unit tests, unit test build file; unit tests should build and run at this point
+3. **Integration/Build**: .dec, .dsc, .fdf, (.yml) configuration files, integration tests; code added to platform and
+   affects downstream consumers
+
+By breaking the pull request into these three categories, the pull request reviewers can digest each piece
+independently.
+
+If your commits are still very large after adhering to these categories, consider further breaking the pull request
+down by library/driver; break each component into its own commit.
+
+#### Implementation Limits
+
+Implementation is ultimately composed of functions as logical units of code.
+
+To help maintainers review the code and improve long-term maintainability, limit functions to 60 lines of code. If your
+function exceeds 60 lines of code, it likely has also exceeded a single responsibility and should be broken up.
+
+Files are easier to review and maintain if they contain functions that serves similar purpose. Limit files to around
+1,000 lines of code (excluding comments). If your file exceeds 1,000 lines of code, it may have functions that should
+be split into separate files.
+
+---
+
+By following these guidelines, your pull requests will be reviewed faster, and you'll avoid being asked to refactor the
+code to follow the guidelines.
+
+Feel free to create a draft pull request and ask for suggestions on how to split the pull request if you are unsure.
+
 ## Thank You
 
 Thank you for your interest in Project Mu and taking the time to contribute!

.sync/github_templates/pull_requests/pull_request_template.md

@@ -1,3 +1,9 @@
+# Preface
+
+Please ensure you have read the [contribution docs](https://github.com/microsoft/mu/blob/master/CONTRIBUTING.md) prior
+to submitting the pull request. In particular,
+[pull request guidelines](https://github.com/microsoft/mu/blob/master/CONTRIBUTING.md#pull-request-best-practices).
+
 ## Description
 
 <_Please include a description of the change and why this change was made._>