Document pub telemetry

CHANGELOG.md

 ## 1.23.0
 
 ### Language
 * Allow using URI strings in `part of` declarations to refer to the
   importing library.
 
 ### Core library changes
 
 * `dart:core`
   * Added `Uri.isScheme` function to check the scheme of a URI.
     Example: `uri.isScheme("http")`. Ignores case when comparing.
   * Make `UriData.parse` validate its input better.
     If the data is base-64 encoded, the data is normalized wrt.
     alphabet and padding, and it contains invalid base-64 data,
     parsing fails. Also normalizes non-base-64 data.
 * `dart:io`
   * Added functions `File.lastAccessed`, `File.lastAccessedSync`,
     `File.setLastModified`, `File.setLastModifiedSync`, `File.setLastAccessed`,
     and `File.setLastAccessedSync`.
-  * Added Added `{Stdin,Stdout}.supportsAnsiEscapes`.
+  * Added `{Stdin,Stdout}.supportsAnsiEscapes`.
 
 ### Dart VM
 * Calls to `print()` and `Stdout.write*()` now correctly print unicode
   characters to the console on Windows. Calls to `Stdout.add*()` behave as
   before.
 
 ### Tool changes
 
 * Analysis
   * `dartanalyzer` now follows the same rules as the analysis server to find
@@ skipping 16 matching lines @@
 
 * Dartium, dart2js, and DDC
 
   * Imports to `dart:io` are allowed, but the imported library is not supported
     and will likely fail on most APIs at runtime. This change was made as a
     stopgap measure to make it easier to write libraries that share code between
     platforms (like package `http`). This might change again when configuration
     specific imports are supported.
 
 * Pub
+  * Now sends telemetry data to `pub.dartlang.org` to allow better understanding
+    of why a particular package is being accessed.
   * `pub publish`
     * Warns if a package imports a package that's not a dependency from within
       `lib/` or `bin/`, or a package that's not a dev dependency from within
       `test/` or `tool/`.
     * No longer produces "UID too large" errors on OS X. All packages are now
       uploaded with the user and group names set to "pub".
     * No longer fails with a stack overflow when uploading a package that uses
       Git submodules.
   * `pub get` and `pub upgrade`
     * Produce more informative error messages if they're run directly in a
@@ skipping 1668 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.