docs: Add info describing model commit messages.

docs/code_contribution_guidelines.md

@@ -6,6 +6,7 @@
 4.1. [Share Early, Share Often](#ShareEarly)<br />
 4.2. [Testing](#Testing)<br />
 4.3. [Code Documentation and Commenting](#CodeDocumentation)<br />
+4.4. [Model Git Commit Messages](#ModelGitCommitMessages)<br />
 5. [Code Approval Process](#CodeApproval)<br />
 5.1 [Code Review](#CodeReview)<br />
 5.2 [Rework Code (if needed)](#CodeRework)<br />
@@ -194,6 +195,52 @@ if amt < 5460 {
 but it was left as a magic number to show how much of a difference a good
 comment can make.
 
+<a name="ModelGitCommitMessages" />
+### 4.4 Code Documentation and Commenting
+
+This project prefers to keep a clean commit history with well-formed commit
+messages.  This section illustrates a model commit message and provides a bit
+of background for it.  This content was originally created by Tim Pope and made
+available on his website, however that website is no longer active, so it is
+being provided here.
+
+Here’s a model Git commit message:
+
+```
+Short (50 chars or less) summary of changes
+
+More detailed explanatory text, if necessary.  Wrap it to about 72
+characters or so.  In some contexts, the first line is treated as the
+subject of an email and the rest of the text as the body.  The blank
+line separating the summary from the body is critical (unless you omit
+the body entirely); tools like rebase can get confused if you run the
+two together.
+
+Write your commit message in the present tense: "Fix bug" and not "Fixed
+bug."  This convention matches up with commit messages generated by
+commands like git merge and git revert.
+
+Further paragraphs come after blank lines.
+
+- Bullet points are okay, too
+- Typically a hyphen or asterisk is used for the bullet, preceded by a
+  single space, with blank lines in between, but conventions vary here
+- Use a hanging indent
+```
+
+Here are some of the reasons why wrapping your commit messages to 72 columns is
+a good thing.
+
+- git log doesn’t do any special special wrapping of the commit messages. With
+  the default pager of less -S, this means your paragraphs flow far off the edge
+  of the screen, making them difficult to read. On an 80 column terminal, if we
+  subtract 4 columns for the indent on the left and 4 more for symmetry on the
+  right, we’re left with 72 columns.
+- git format-patch --stdout converts a series of commits to a series of emails,
+  using the messages for the message body.  Good email netiquette dictates we
+  wrap our plain text emails such that there’s room for a few levels of nested
+  reply indicators without overflow in an 80 column terminal.
+
 <a name="CodeApproval" />
 ### 5. Code Approval Process