doc: getting_started: fix outdated west init --mr information

You can no longer use 'west init --mr SHA'; this has been the case
since west v0.11.0. Update the getting started guide for manual
installation accordingly.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

doc/nrf/installation/installing.rst

@@ -286,7 +286,6 @@ To clone the repositories, complete the following steps:
      You can find the tag in the :ref:`release_notes` of the release.
    * To work with a :ref:`development tag <intro_vers_revs>`, the identifier is the corresponding tag (for example, ``v1.2.99-dev1``)
    * To work with a branch, the identifier is the branch name (for example, ``main`` to work with the latest state of development).
-   * To work with a specific state, the identifier is the SHA (for example, ``224bee9055d986fe2677149b8cbda0ff10650a6e``).
 
 #. On the command line, go to the :file:`ncs` folder (``cd ncs``) and initialize west with the revision of the |NCS| that you want to check out, replacing *nRFConnectSDK_revision* with the identifier:
 
@@ -347,6 +346,14 @@ This is a simplified structure preview.
 There are additional folders, and the structure might change over time.
 The full set of repositories and folders is defined in the manifest file.
 
+In order to change the state of development you want to use to a different revision, enter the following commands from the :file:`nrf` directory you created earlier::
+
+  git checkout *next_revision*
+  west update
+
+In this case, *next_revision* can be either a SHA (for example, ``224bee9055d986fe2677149b8cbda0ff10650a6e``), a branch, or a tag name.
+You can use any revision of the sdk-nrf repository that is available on your local file system.
+
 .. _additional_deps:
 
 .. rst-class:: numbered-step

doc/nrf/installation/updating.rst

@@ -76,12 +76,14 @@ To switch to release |release| of the |NCS|, enter the following commands in the
    git checkout |release|
    west update
 
-To update to a particular revision (SHA), make sure that you have that particular revision locally before you check it out (by running ``git fetch origin``)::
+To update to a particular revision, make sure that you have that particular revision on your local file system before you check it out (by running ``git fetch origin``)::
 
    git fetch origin
-   git checkout 224bee9055d986fe2677149b8cbda0ff10650a6e
+   git checkout *next_revision*
    west update
 
+In this case, *next_revision* can be either a SHA (for example, ``224bee9055d986fe2677149b8cbda0ff10650a6e``), a branch, or a tag name.
+
 To switch to the latest state of development, enter the following commands::
 
    git fetch origin