Add guideline for Permission denied (publickey)

Add more guideline for Permission denied (publickey) status.

Fixing flake8 error in an unrelated doc to pass gating.

Change-Id: I3dccf05fa2f9f23d52bb0dd46e27f83877986b24

doc/doc-contrib-guide/source/quickstart/first-timers.rst

@@ -278,6 +278,24 @@ git and git review
 
   On Windows, look for it in the same location.
 
+  If you still received a ``Permission denied (publickey)`` message,
+  you might need to check if you hit ``no mutual signature algorithm``.
+  Any given system running OpenSSH 8.8 or newer as this release disables RSA
+  signatures using the SHA-1 hash algorithm by default.
+  Try to run the following command:
+
+  .. code-block:: console
+
+     ssh -vv -p 29418 {username}@review.opendev.org
+
+  If you saw ``no mutual signature algorithm``,
+  you need to consider using another algorithm instead of RSA.
+  For example, use ``ed25519`` to generate your key and upload ``id_ed25519.pub``.
+
+  .. code-block:: console
+
+     ssh-keygen -t ed25519 -C "your_email@example.com"
+
 * Merge conflict, rebase required
 
   Sometimes your change creates a merge conflict with another patch.

doc/install-guide/source/environment-packages-rdo.rst

@@ -184,7 +184,8 @@ Prerequisites
   Red Hat Subscription Management. For more information on registering a RHEL 7
   system, see the `Red Hat Enterprise Linux 7 System Administrator's Guide
   <https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/System_Administrators_Guide/part-Subscription_and_Support.html>`_
-  For more information on registering a RHEL 8 system, see the `Red Hat Enterprise Linux 8 Installation Guide
+  For more information on registering a RHEL 8 system, see the
+  `Red Hat Enterprise Linux 8 Installation Guide
   <https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/8/html/performing_a_standard_rhel_installation/post-installation-tasks_installing-rhel>`_.
 
 * Enable the required repositories: