Add 2.0.0 relnotes to RELEASE.md

RELEASE.md

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+# Release 2.0.0
+
+The 2.0 minor series tracks TensorFlow 2.0.
+
+## Breaking changes
+
+- TensorBoard now serves on localhost only by default to avoid unintentional
+  overexposure. To expose TensorBoard to the network, either use a proxy, bind
+  to a specific hostname or IP address by using the `--host` flag, or explicitly
+  enable the previous behavior of binding on all network interfaces by passing
+  the flag `--bind_all`. See PR #2589.
+
+- The `--logdir` flag no longer supports passing multiple comma-delimited paths,
+  which means that it now *supports* paths containing literal comma and colon
+  characters, like `./logs/m=10,n=20,lr=0.001` or `./logs/run_12:30:15`. To
+  mimic the old behavior, prefer using a tree of symlinks as it works with more
+  plugins, but as a fallback the flag `--logdir_spec` exposes the old behavior.
+  See PR #2664.
+
+- Projector plugin `visualize_embeddings()` API now takes `logdir` as its first
+  parameter rather than `writer` (which only supported TF 1.x summary writers).
+  For backwards compatibility TF 1.x writers will still be accepted, but passing
+  the logdir explicitly is preferred since it works without any dependency on
+  TF 1.x or 2.x summary writing. See PR #2665.
+
+- The namespace `tensorboard.summary.*` now aliases the summary API symbols in
+  `tensorboard.summary.v2.*` rather than those in `tensorboard.summary.v1.*`.
+  The old symbols can still be accessed under the `.v1` names. Note that the
+  new v2 API symbols are exposed in TF 2.0 as the new `tf.summary.*` API and
+  this is normally how they should be used. See PR #2670.
+
+## Features
+
+- Smarter log directory polling can be used by passing `--reload_multifile=true`
+  to poll all "active" event files in a directory rather than only the last one.
+  This avoids problems where data written to the non-last file never appears.
+  See PR #1867 for details, including how to adjust the "active" threshold.
+
+- What-If Tool now can sort PD plots by interestingness (#2461)
+
+
 # Release 1.15.0
 
 The 1.15 minor series tracks TensorFlow 1.15.