Update readme table and make_readme_table (#4077)

README.md

 | **Version** | **Release Date** | **Source** | **Documentation** | **Download** |
 |:-------:|:------:|:-------------:|:-------:|:------------:|
 | **master (unstable)** | -- | [source](https://github.com/Unity-Technologies/ml-agents/tree/master) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/master/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/master.zip) |
-| **Release 2** | **May 20, 2020** | **[source](https://github.com/Unity-Technologies/ml-agents/tree/release_2)** | **[docs](https://github.com/Unity-Technologies/ml-agents/tree/release_2/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/release_2.zip)** |
-| **Release 1** | April 30, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/release_1) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/release_1/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/release_1.zip) |
+| **Release 3** | **June 10, 2020** | **[source](https://github.com/Unity-Technologies/ml-agents/tree/release_3)** | **[docs](https://github.com/Unity-Technologies/ml-agents/tree/release_3_docs/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/release_3.zip)** |
+| **Release 2** | May 20, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/release_2) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/release_2_docs/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/release_2.zip) |
+| **Release 1** | April 30, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/release_1) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/release_1_docs/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/release_1.zip) |
 | **0.15.1** | March 30, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.15.1) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.15.1/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.15.1.zip) |
 | **0.15.0** | March 18, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.15.0) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.15.0/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.15.0.zip) |
 | **0.14.1** | February 26, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/0.14.1) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/0.14.1/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/0.14.1.zip) |

utils/make_readme_table.py

 
 def table_line(display_name, name, date, bold=False):
     bold_str = "**" if bold else ""
-    return f"| **{display_name}** | {bold_str}{date}{bold_str} | {bold_str}[source](https://github.com/Unity-Technologies/ml-agents/tree/{name}){bold_str} | {bold_str}[docs](https://github.com/Unity-Technologies/ml-agents/tree/{name}/docs/Readme.md){bold_str} | {bold_str}[download](https://github.com/Unity-Technologies/ml-agents/archive/{name}.zip){bold_str} |"  # noqa
+    # For release_X branches, docs are on a separate tag.
+    if name.startswith("release"):
+        docs_name = name + "_docs"
+    else:
+        docs_name = name
+    return f"| **{display_name}** | {bold_str}{date}{bold_str} | {bold_str}[source](https://github.com/Unity-Technologies/ml-agents/tree/{name}){bold_str} | {bold_str}[docs](https://github.com/Unity-Technologies/ml-agents/tree/{docs_name}/docs/Readme.md){bold_str} | {bold_str}[download](https://github.com/Unity-Technologies/ml-agents/archive/{name}.zip){bold_str} |"  # noqa
 
 
 class ReleaseInfo(NamedTuple):
     ReleaseInfo.from_simple_tag("0.15.1", "March 30, 2020"),
     ReleaseInfo("release_1", "1.0.0", "0.16.0", "April 30, 2020"),
     ReleaseInfo("release_2", "1.0.2", "0.16.1", "May 20, 2020"),
+    ReleaseInfo("release_3", "1.1.0", "0.17.0", "June 10, 2020"),
 ]
 
 MAX_DAYS = 150  # do not print releases older than this many days