add 1.0.8 to the release table (#5398)

README.md

 | **Version** | **Release Date** | **Source** | **Documentation** | **Download** | **Python Package** | **Unity Package** |
 |:-------:|:------:|:-------------:|:-------:|:------------:|:------------:|:------------:|
 | **main (unstable)** | -- | [source](https://github.com/Unity-Technologies/ml-agents/tree/main) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/main/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/main.zip) | -- | -- |
+| **Verified Package 1.0.8** | **May 26, 2021** | **[source](https://github.com/Unity-Technologies/ml-agents/tree/com.unity.ml-agents_1.0.8)** | **[docs](https://github.com/Unity-Technologies/ml-agents/blob/release_2_verified_docs/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/com.unity.ml-agents_1.0.8.zip)** | **[0.16.1](https://pypi.org/project/mlagents/0.16.1/)** | **[1.0.8](https://docs.unity3d.com/Packages/com.unity.ml-agents@1.0/manual/index.html)** |
-| **Verified Package 1.0.7** | **March 8, 2021** | **[source](https://github.com/Unity-Technologies/ml-agents/tree/com.unity.ml-agents_1.0.7)** | **[docs](https://github.com/Unity-Technologies/ml-agents/blob/release_2_verified_docs/docs/Readme.md)** | **[download](https://github.com/Unity-Technologies/ml-agents/archive/com.unity.ml-agents_1.0.7.zip)** | **[0.16.1](https://pypi.org/project/mlagents/0.16.1/)** | **[1.0.7](https://docs.unity3d.com/Packages/com.unity.ml-agents@1.0/manual/index.html)** |
+| **Verified Package 1.0.7** | March 8, 2021 | [source](https://github.com/Unity-Technologies/ml-agents/tree/com.unity.ml-agents_1.0.7) | [docs](https://github.com/Unity-Technologies/ml-agents/blob/release_2_verified_docs/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/com.unity.ml-agents_1.0.7.zip) | [0.16.1](https://pypi.org/project/mlagents/0.16.1/) | [1.0.7](https://docs.unity3d.com/Packages/com.unity.ml-agents@1.0/manual/index.html) |
-| **Release 12** | December 22, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/release_12) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/release_12_docs/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/release_12.zip) | [0.23.0](https://pypi.org/project/mlagents/0.23.0/) | [1.7.2](https://docs.unity3d.com/Packages/com.unity.ml-agents@1.7/manual/index.html) |
-| **Release 11** | December 21, 2020 | [source](https://github.com/Unity-Technologies/ml-agents/tree/release_11) | [docs](https://github.com/Unity-Technologies/ml-agents/tree/release_11_docs/docs/Readme.md) | [download](https://github.com/Unity-Technologies/ml-agents/archive/release_11.zip) | [0.23.0](https://pypi.org/project/mlagents/0.23.0/) | [1.7.0](https://docs.unity3d.com/Packages/com.unity.ml-agents@1.7/manual/index.html) |
 
 If you are a researcher interested in a discussion of Unity as an AI platform,
 see a pre-print of our

utils/make_readme_table.py

     ReleaseInfo("release_16", "1.9.1", "0.25.1", "April 13, 2021"),
     ReleaseInfo("release_17", "2.0.0", "0.26.0", "April 22, 2021"),
     # Verified releases
+    ReleaseInfo("", "1.0.8", "0.16.1", "May 26, 2021", is_verified=True),
     ReleaseInfo("", "1.0.7", "0.16.1", "March 8, 2021", is_verified=True),
     ReleaseInfo("", "1.0.6", "0.16.1", "November 16, 2020", is_verified=True),
     ReleaseInfo("", "1.0.5", "0.16.1", "September 23, 2020", is_verified=True),