website: Updated contributed guidelines with `stable` branch.

Change-Id: Ib708ba775862f15645adb9cb3b4155a9bf5951f2
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/35435
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
diff --git a/_pages/contributing.md b/_pages/contributing.md
index 4e9f274..c9ae8ea 100644
--- a/_pages/contributing.md
+++ b/_pages/contributing.md
@@ -7,7 +7,7 @@
 
 This document serves as a beginners guide to contributing to gem5. If questions
 arise while following this guide, we advise consulting [CONTRIBUTING.md](
-https://gem5.googlesource.com/public/gem5/+/refs/heads/master/CONTRIBUTING.md)
+https://gem5.googlesource.com/public/gem5/+/refs/heads/stable/CONTRIBUTING.md)
 which contains more details on how to contribute to gem5.
 
 The following subsections outline, in order, the steps involved in contributing
@@ -48,15 +48,15 @@
 git clone https://gem5.googlesource.com/public/gem5
 ```
 
-### master-as-stable / develop branch
+### stable / develop branch
 
-By default, the git repo will have the `master` branch checked-out. The
-`master` branch is considered the gem5 stable release branch. I.e., the HEAD
+By default, the git repo will have the `stable` branch checked-out. The
+`stable` branch is the gem5 stable release branch. I.e., the HEAD
 of this branch contains the latest stable release of gem5. (execute `git tag`
-on the `master` branch to see the list of stable releases. A particular
+on the `stable` branch to see the list of stable releases. A particular
 release may be checked out by executing `git checkout <release>`). As the
-`master` branch only contains officially released gem5 code **contributors
-should not develop changes on top of the `master` branch** they should instead
+`stable` branch only contains officially released gem5 code **contributors
+should not develop changes on top of the `stable` branch** they should instead
 **develop changes on top of the `develop` branch**.
 
 To checkout the `develop` branch:
@@ -194,7 +194,7 @@
 the "header". The header starts with a tag (or tags, separated by a comma),
 then a colon. Which tags are used depend on which components of gem5
 you have modified. **Please refer to the [MAINTAINERS.md](
-https://gem5.googlesource.com/public/gem5/+/refs/heads/master/MAINTAINERS) for
+https://gem5.googlesource.com/public/gem5/+/refs/heads/stable/MAINTAINERS) for
 a comprehensive list of accepted tags**. After this colon a short description
 of the commit must be provided. **This header line must not exceed 65
 characters**.
@@ -266,7 +266,7 @@
 components you have modified should be added as reviewers. These should
 correspond to the tags you included in the commit header. **Please consult
 [MAINTAINERS.md](
-https://gem5.googlesource.com/public/gem5/+/refs/heads/master/MAINTAINERS) to
+https://gem5.googlesource.com/public/gem5/+/refs/heads/stable/MAINTAINERS) to
 see who maintains which component**. As an example, for a commit with a header
 of `tests,arch : This is testing the arch component` then the maintainers for
 both `tests` and `arch` should be included as reviewers.
@@ -347,5 +347,5 @@
 that the task has been completed.
 
 Stable releases of gem5 are published three times per year. Therefore, a change
-successfully submitted to the `develop` branch will be merged into the `master`
+successfully submitted to the `develop` branch will be merged into the `stable`
 branch within three to four months after submission.