Update readme

[Berk-Tosun]

Remove misleading Python 3.8 statement from installation instructions. Python3.8 pip cannot install tensorflow1.x.

And it will stay that way:
tensorflow/tensorflow#39768 (comment)

[Berk-Tosun]

Regarding requirements update, protobuf version must be specified, otherwise I get the following error while running:

python3 -m motion_imitation.examples.test_env_gui --robot_type=A1 --motor_control_mode=Position --on_rack=True

error:
pybullet build time: May 20 2022 19:43:01
Traceback (most recent call last):
File "/home/berk/miniconda3/envs/py37/lib/python3.7/runpy.py", line 193, in _run_module_as_main
"main", mod_spec)
File "/home/berk/miniconda3/envs/py37/lib/python3.7/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/home/berk/Documents/msc_thesis/ws2/motion_imitation/motion_imitation/examples/test_env_gui.py", line 15, in
from motion_imitation.envs import env_builder
File "/home/berk/Documents/msc_thesis/ws2/motion_imitation/motion_imitation/envs/env_builder.py", line 37, in
from motion_imitation.envs.utilities import controllable_env_randomizer_from_config
File "/home/berk/Documents/msc_thesis/ws2/motion_imitation/motion_imitation/envs/utilities/controllable_env_randomizer_from_config.py", line 32, in
import tensorflow as tf
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow/init.py", line 102, in
from tensorflow_core import *
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/init.py", line 28, in
from tensorflow.python import pywrap_tensorflow # pylint: disable=unused-import
File "", line 1019, in _handle_fromlist
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow/init.py", line 50, in getattr
module = self._load()
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow/init.py", line 44, in _load
module = _importlib.import_module(self.name)
File "/home/berk/miniconda3/envs/py37/lib/python3.7/importlib/init.py", line 127, in import_module
return _bootstrap._gcd_import(name[level:], package, level)
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/python/init.py", line 52, in
from tensorflow.core.framework.graph_pb2 import *
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/core/framework/graph_pb2.py", line 16, in
from tensorflow.core.framework import node_def_pb2 as tensorflow_dot_core_dot_framework_dot_node__def__pb2
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/core/framework/node_def_pb2.py", line 16, in
from tensorflow.core.framework import attr_value_pb2 as tensorflow_dot_core_dot_framework_dot_attr__value__pb2
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/core/framework/attr_value_pb2.py", line 16, in
from tensorflow.core.framework import tensor_pb2 as tensorflow_dot_core_dot_framework_dot_tensor__pb2
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/core/framework/tensor_pb2.py", line 16, in
from tensorflow.core.framework import resource_handle_pb2 as tensorflow_dot_core_dot_framework_dot_resource__handle__pb2
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/core/framework/resource_handle_pb2.py", line 16, in
from tensorflow.core.framework import tensor_shape_pb2 as tensorflow_dot_core_dot_framework_dot_tensor__shape__pb2
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/tensorflow_core/core/framework/tensor_shape_pb2.py", line 42, in
serialized_options=None, file=DESCRIPTOR),
File "/home/berk/miniconda3/envs/py37/lib/python3.7/site-packages/google/protobuf/descriptor.py", line 560, in new
_message.Message._CheckCalledFromGeneratedFile()
TypeError: Descriptors cannot not be created directly.
If this call came from a _pb2.py file, your generated code is out of date and must be regenerated with protoc >= 3.19.0.
If you cannot immediately regenerate your protos, some other possible workarounds are:

1. Downgrade the protobuf package to 3.20.x or lower.
2. Set PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=python (but this will use pure-Python parsing and will be much slower).

More information: https://developers.google.com/protocol-buffers/docs/news/2022-05-06#python-updates