started a pr about rnn hidsize

[alexunderch]

1. Fixed the Dockerfile — i.e. added important env. variables and eased development interaction with git;
2. Changed IPPO baseline for SMAX — i.e. made it independent of rnn hidden_size. Say if the fix actually works and then I can implement it everywhere in IPPO/MAPPO baselines (in configs there is GRU_HIDDEN_SIZE variable (name is arbitrary), with default value of 256). Default experiment is accessible via:

   python ippo_rnn_smax.py GRU_HIDDEN_SIZE=128

3. now WANDB_ENTITY could be parsed directly from the docker environment
4. A small fix in the walkthrough colab — i.e. a note about runtime reboot after the installation.

If I have to add tests or smth, ping me.

[amacrutherford]

looks great! Have run the RNN change and results look reasonable