docs: Add version reference and compatibility matrix to README

It probably does not hurt to include the current version in the
README. To make sure that it gets proper updates upon the release of
a new version, add a reference to the README to the bumpversion
configuration, as well.

In addition, add a version compatibility matrix for older Open edX
releases.

.bumpversion.cfg

@@ -12,3 +12,5 @@ serialize =
 [bumpversion:file:Changelog.md]
 search = Unreleased
 replace = Version {new_version} ({now:%Y-%m-%d})
+
+[bumpversion:file:README.md]

README.md

@@ -14,18 +14,23 @@ browser-based connection mechanism, which includes the ability to connect to
 graphical user environments (via VNC and RDP), in addition to terminals (via
 SSH).
 
+## Version compatibility matrix
 
-> **Important changes in version 7**
->
-> Version 7 of this XBlock is intended to be deployed on Open edX
-> Nutmeg, with [Tutor](https://docs.tutor.overhang.io/) version 14.x
-> and [the `hastexo` Tutor
-> plugin](https://github.com/hastexo/tutor-contrib-hastexo), version
-> 1.x.
->
-> Instructions for deploying this XBlock with Tutor can be found
-> below, in the [Deployment with Tutor](#deployment-with-tutor)
-> section.
+You must install a supported release of this XBlock to match the
+Open edX and [Tutor](https://docs.tutor.overhang.io/) version you are
+deploying. If you are installing this plugin from a branch in this Git
+repository, you must select the appropriate one:
+
+| Open edX release | Tutor version | XBlock version | XBlock branch |
+|------------------|---------------|----------------|---------------|
+| Maple            | `>=13.2, <14` | `>=6.0, <7.0`  | `stable-6.0`  |
+| Nutmeg           | `>=14.0, <15` | `>=7.0`        | `master`      |
+| Olive            | `>=15.0, <16` | `>=7.5`        | `master`      |
+| Palm             | `>=16.0, <17` | `>=7.5`        | `master`      |
+
+Instructions for deploying this XBlock with Tutor can be found
+below, in the [Deployment with Tutor](#deployment-with-tutor)
+section.
 
 ## Purpose
 
@@ -60,7 +65,7 @@ two steps:
    `OPENEDX_EXTRA_PIP_REQUIREMENTS` list in `config.yml`:
    ```
    OPENEDX_EXTRA_PIP_REQUIREMENTS:
-     - "hastexo-xblock>=7"
+     - "hastexo-xblock==7.7.0"
    ```
    For additional information, please refer to the [official
    documentation](https://docs.tutor.overhang.io/configuration.html#installing-extra-xblocks-and-requirements).