Miscellaneous minor documentation updates

CONTRIBUTING.md

@@ -39,7 +39,7 @@ anyone can see the source, but only ISC employees have commit access.
 In the past, the source could only be seen once ISC had published
 a release; read access to the source repository was restricted just
 as commit access was.  That has changed, as ISC now provides a
-public git mirror to the BIND source tree (see below).
+public git repository of the BIND source tree (see below).
 
 At ISC, we're committed to
 building communities that are welcoming and inclusive: environments where people
@@ -55,14 +55,12 @@ the industry.
 Public BIND releases are always available from the
 [ISC FTP site](ftp://ftp.isc.org/isc/bind9).
 
-A public-access GIT repository is also available at
-[https://gitlab.isc.org](https://gitlab.isc.org).
-This repository is a mirror, updated several times per day, of the
-source repository maintained by ISC.  It contains all the public release
-branches; upcoming releases can be viewed in their current state at any
-time.  It does *not* contain development branches or unreviewed work in
-progress.  Commits which address security vulnerablilities are withheld
-until after public disclosure.
+A public-access git repository is also available at
+[https://gitlab.isc.org](https://gitlab.isc.org).  This repository
+contains all public release branches. Upcoming releases can be viewed in
+their current state at any time.  Short-lived development branches
+contain unreviewed work in progress.  Commits which address security
+vulnerablilities are withheld until after public disclosure.
 
 You can browse the source online via
 [https://gitlab.isc.org/isc-projects/bind9](https://gitlab.isc.org/isc-projects/bind9)

PLATFORMS.md

@@ -61,7 +61,7 @@ The following are platforms on which BIND is known to build and run.
 ISC makes every effort to fix bugs on these platforms, but may be unable to
 do so quickly due to lack of hardware, less familiarity on the part of
 engineering staff, and other constraints. With the exception of Windows
-Server 2012 R2, none of these are tested regularly by ISC.
+Server 2016, none of these are tested regularly by ISC.
 
 * Windows Server 2012 R2, 2016 / x64
 * Windows 10 / x64

README.md

@@ -15,7 +15,6 @@
 1. [Introduction](#intro)
 1. [Reporting bugs and getting help](#help)
 1. [Contributing to BIND](#contrib)
-1. [BIND 9.17 features](#features)
 1. [Building BIND](#build)
 1. [macOS](#macos)
 1. [Dependencies](#dependencies)
@@ -125,16 +124,6 @@ If you prefer, you may also submit code by opening a
 including your patch as an attachment, preferably generated by
 `git format-patch`.
 
-### <a name="features"/> BIND 9.17 features
-
-BIND 9.17 is the newest development branch of BIND 9. It includes a
-number of changes from BIND 9.16 and earlier releases. New features include:
-
-* The new option `max-ixfr-ratio` to limit the size of outgoing IXFR responses
-  before falling back to full zone transfers.
-* `rndc nta -d` and `rndc secroots` now include `validate-except` entries
-  when listing negative trust anchors.
-
 ### <a name="build"/> Building BIND 9
 
 At a minimum, BIND requires a Unix or Linux system with an ANSI C compiler,