message: Added README.md about add_model.py
diff: A set of tools to record the conditions (code, parameters, ...) and agregate the results of many evaluation runs.
  +## add_model.py and evaluator
  +
  +Used to add Player(model weights + flags) to models_to_eval CBT.
  +
  +#TODO(amj): test this code snippit
  +```bash
  +# From minigo/
  +source cluster/common.sh
  +export PROJECT=that one thing
  +export SGF_BUCKET_NAME=minigo-pub
  +
  +mkdir -p temp && cd temp
  +
  +# Alphabetical for gsutil ls to work below
  +export MODEL_A=369a0424c4
  +export MODEL_B=52eb46008a
  +export CBT_TABLE=$CBT_MODEL_EVAL_TABLE
  +
  +../cluster/evaluator/evaluator_ringmaster_wrapper.sh
  +
  +ls
  +gsutil ls gs://minigo-pub/eval_server/models/games/${MODEL_A}_vs_${MODEL_B}
  +cbt -project "$PROJECT" -instance "$CBT_INSTANCE" read "$CBT_TABLE"
  +```
  ## Goals
  1. Reproducability (see https://github.com/tensorflow/minigo/issues/591)
  @@ -11,11 +35,11 @@ A set of tools to record the conditions (code, parameters, ...) and agregate the
  3. Store all data in a common repository with common naming scheme
  4. Be easy to extend piecewise as needed
  1. Be backwards compatible as often as possible
  -5. Guide us towards gating (see https://github.com/tensorflow/minigo/issues/570_
  +5. Guide us towards gating (see https://github.com/tensorflow/minigo/issues/570)
  ## Methodology
  -* Results table / Evaluation (https://github.com/tensorflow/minigo/issues/591)
  +* Results table / Evaluation [#591](https://github.com/tensorflow/minigo/issues/591)
  - Uses bigtable tag [#590](https://github.com/tensorflow/minigo/pull/590) to name a comparison
  - Use [launch_eval.py](https://github.com/tensorflow/minigo/blob/master/cluster/evaluator/launch_eval.py) and record command (somewhere)
  - Directory structure
  @@ -28,6 +52,6 @@ A set of tools to record the conditions (code, parameters, ...) and agregate the
  - Command line invocation of `launch_eval.py`
  - metadata (json?, contents TBD)
  - [optional] command_flags
  - - [future] \<shorttag>_ringmaster.ctl (see https://github.com/tensorflow/minigo/issues/544)
  + - [future] \<shorttag>_ringmaster.ctl (see [#544](https://github.com/tensorflow/minigo/issues/544))
  - [future] branch (github branch where code can be found)
  - [future] diff.patch
  