Fix PT-1605, 3.0 version, documenting data collected... (#359)

* Fix PT-1605, 3.0 version, documenting data collected with --version-check

* Made text more general and less PT based

docs/version-check.rst

@@ -0,0 +1,67 @@
+.. _version-check:
+
+================================================================================
+Version Checking
+================================================================================
+
+Complex software projects (such as MySQL flavors) always have versions with
+minor or major compatibility problems, regressions and bugs, etc. It is too
+difficult to take care about all these compatibility nuances for a human, and
+this is the reason for a |version-check| feature to exist.
+
+The feature allows compatible tools to query the Version Check database and
+print advice on any potential risks associated with any of the relevant
+software versions.
+
+Usage
+-----
+
+*Version Check* was implemented in |pt| 2.1.4, and was enabled by default in
+version 2.2.1. Currently it is supported by most tools in |pt|, |pxb|, and
+|pmm|.
+
+Being called with Version Check enabled,the tool that supports this feature
+connects to a dedicated Percona server via a secure HTTPS channel. It checks
+its own version to query the server for possible updates, and also checks
+versions of the following software:
+
+* operating system
+* Percona Monitoring and Management (PMM)
+* MySQL
+* Perl
+* MySQL driver for Perl (DBD::mysql)
+* Percona Toolkit
+
+Then it checks for and warns about versions with known problems.
+
+To guide the development of future |version-check| requirements, each request
+is logged by the server. Stored information includes software version numbers
+and the unique ID of a checked system. The ID is generated either at
+installation or when the |version-check| query is done for the first time.
+
+.. note::
+
+   Prior to version 3.0.7 of |pt|, the system ID was calculated as an MD5 hash
+   of the hostname, and starting from |pt| 3.0.7 it is generated as a random
+   number.
+
+Disabling Version Check
+-----------------------
+
+Although the |version-check| feature does not collect any personal information,
+you might prefer to disable this feature, either onetime or permanently.
+To disable it onetime, use ``--no-version-check`` option when invoking the tool
+from a Percona product which supports it.
+
+Disabling |version-check| permanently can be done by placing
+``--no-version-check`` option into the configuration file of a Percona product
+(see correspondent documentation for exact file name and syntax). For example,
+in case of |pt| `this can be done <https://www.percona.com/doc/percona-toolkit/LATEST/configuration_files.html>`_ in a global configuration file ``/etc/percona-toolkit/percona-toolkit.conf``::
+
+  # Disable Version Check for all tools:
+  no-version-check
+
+.. |pmm| replace:: PMM (Percona Monitoring and Management)
+.. |pt| replace:: Percona Toolkit
+.. |pxb| replace:: Percona XtraBackup
+.. |version-check| replace:: *version checking*