update installation instructions in README

* suggest `pip install -e .` instead of editing the PYTHONPATH and PATH environment variables (which does not work nicely in Windows and/or VSCode)
* suggest venv instead of `--user`
* suggest `pip` instead of `pip3` (Python2 is not supported anyway)
* delete details about the C++11 compiler for ufal.udpipe

Author: martinpopel

README.md

@@ -7,27 +7,23 @@ Python framework for processing Universal Dependencies data
 
 ## Requirements
 - You need Python 3.9 or higher.
-- If the [ufal.udpipe](https://pypi.python.org/pypi/ufal.udpipe/) parser is needed,
-  make sure you have a C++11 compiler (e.g. [g++ 4.7 or newer](.travis.yml#L9))
-  and install UDPipe with `pip3 install --user --upgrade ufal.udpipe`.
+- It is recommended to install Udapi in a Python virtual environment.
+- If you need the [ufal.udpipe](https://pypi.python.org/pypi/ufal.udpipe/) parser (to be used from Udapi)
+  install it (with `pip install --upgrade ufal.udpipe`).
 
 ## Install Udapi for developers
-Let's clone the git repo to `~/udapi-python/`, install dependencies
-and setup `$PATH` and `$PYTHONPATH` accordingly.
+Let's clone the git repo e.g. to `~/udapi-python/` and make an [editable installation](https://setuptools.pypa.io/en/latest/userguide/development_mode.html)
 ```bash
 cd
 git clone https://github.com/udapi/udapi-python.git
-pip3 install --user -r udapi-python/requirements.txt
-echo '## Use Udapi from ~/udapi-python/ ##'                >> ~/.bashrc
-echo 'export PATH="$HOME/udapi-python/bin:$PATH"'          >> ~/.bashrc
-echo 'export PYTHONPATH="$HOME/udapi-python/:$PYTHONPATH"' >> ~/.bashrc
-source ~/.bashrc # or open new bash
+cd udapi-python
+pip install -e .
 ```
 
 ## Install Udapi for users
 This is similar to the above, but installs Udapi from PyPI to the standard (user) Python paths.
 ```
-pip3 install --user --upgrade udapi
+pip install --upgrade udapi
 ```
 Try `udapy -h` to check it is installed correctly.
 If it fails, make sure your `PATH` includes the directory where `pip3` installed the `udapy` script.