chore: update commit guidelines in CONTRIBUTING.md

The commit guidelines are too vague and offer little guidance on
acceptable commit styles. This patch expands on what is acceptable
with some examples of what a commit is supposed to look like.

Signed-off-by: Alano Terblanche <[email protected]>

CONTRIBUTING.md

@@ -134,9 +134,41 @@ committing your changes. Most editors have plug-ins that do this automatically.
 Pull request descriptions should be as clear as possible and include a reference
 to all the issues that they address.
 
-Commit messages must start with a capitalized and short summary (max. 50 chars)
-written in the imperative, followed by an optional, more detailed explanatory
-text which is separated from the summary by an empty line.
+Commit messages must be written in the imperative (max. 72 chars), followed
+by an optional, more detailed explanatory text usually expanding on
+why the work is necessary. The explanatory text should be separated by an
+empty line.
+
+The commit message *could* have a prefix scoping the change, however this is
+not enforced. Common prefixes are `docs: <message>`, `vendor: <message>`,
+`chore: <message>` or the package/area related to the change such as `pkg/foo: <message>`
+or `telemetry: <message>`.
+
+A standard commit.
+```
+Fix the exploding flux capacitor
+
+A call to function A causes the flux capacitor to blow up every time
+the sun and the moon align.
+```
+
+Using a package as prefix.
+```
+pkg/foo: prevent panic in flux capacitor
+
+Calling function A causes the flux capacitor to blow up every time
+the sun and the moon align.
+```
+
+Updating a specific vendored package.
+```
+vendor: github.com/docker/docker 6ac445c42bad (master, v28.0-dev)
+```
+
+Fixing a broken docs link.
+```
+docs: fix style/lint issues in deprecated.md
+```
 
 Code review comments may be added to your pull request. Discuss, then make the
 suggested modifications and push additional commits to your feature branch. Post