Trac #34367: README.md, installation guide: Mention cocalc Docker ima…

…ge instead of sagemath/sagemath image

The sagemath/sagemath image has been broken and semi-abandoned for a
long time. We replace mentions of it by the cocalc image and a link to
https://trac.sagemath.org/wiki/Distribution#Dockerimages

URL: https://trac.sagemath.org/34367
Reported by: mkoeppe
Ticket author(s): Matthias Koeppe
Reviewer(s): Dima Pasechnik

README.md

@@ -21,12 +21,14 @@ Getting Started
 
 The [Sage Installation Guide](https://doc.sagemath.org/html/en/installation/index.html)
 provides a decision tree that guides you to the type of installation
-that will work best for you.
+that will work best for you. This includes building from source,
+obtaining Sage from a package manager, using a container image, or using
+Sage in the cloud.
 
-If you have already cloned the git repository or downloaded the
+**This README contains self-contained instructions for building Sage from source.**
+It assumes that you have already cloned the git repository or downloaded the
 [sources](https://www.sagemath.org/download-source.html) in the form
-of a tarball, please read the self-contained instructions below on how
-to build Sage and work around common issues.
+of a tarball.
 
 If you have questions or encounter problems, please do not hesitate
 to email the [sage-support mailing list](https://groups.google.com/group/sage-support)
@@ -47,15 +49,6 @@ We highly appreciate contributions to Sage that fix portability bugs
 and help port Sage to new platforms; let us know at the [sage-devel
 mailing list](https://groups.google.com/group/sage-devel).
 
-Docker Images
--------------
-
-You can also have a look at our Docker images to run Sage.
-To use these images,
-[install Docker](https://www.docker.com/community-edition#/download)
-and follow the instructions on
-[our Docker Hub page](https://hub.docker.com/r/sagemath/sagemath/).
-
 [Windows] Preparing the Platform
 --------------------------------
 

src/doc/en/installation/index.rst

@@ -130,8 +130,10 @@ In the cloud
 - `CoCalc <https://cocalc.com/>`_: an online service that provides SageMath and
   many other tools.
 
-- On any system that allows you to bring your own Docker images to run in
-  a container:  Use the `Docker image sagemath/sagemath <https://hub.docker.com/r/sagemath/sagemath/>`_.
+- On any system that allows you to bring your own Docker images to run
+  in a container: Use the `Docker image sagemathinc/cocalc
+  <https://hub.docker.com/r/sagemathinc/cocalc>`_ or :trac:`another Docker
+  image providing SageMath <wiki/Distribution#Dockerimages>`.
 
 - `Sage Cell Server <https://sagecell.sagemath.org/>`_: an online service for
   elementary SageMath computations.