Please update installation guide

If I clone this projec then run the zeronet.py, it doesn't work.

Even after I run `sudo pip install -r requirements.txt`, It doesn't works.

```
beenotung:ZeroNet$ ./zeronet.py
- Starting ZeroNet...
ERROR:root:Unhandled exception: No module named gevent
Traceback (most recent call last):
File "./zeronet.py", line 18, in main
import main
File "/home/beenotung/local/opt/ZeroNet/src/main.py", line 9, in
import gevent
ImportError: No module named gevent
Traceback (most recent call last):
File "./zeronet.py", line 91, in
main()
File "./zeronet.py", line 64, in main
traceback.print_exc(file=open(config.log_dir + "/error.log", "a"))
AttributeError: 'Config' object has no attribute 'log_dir'

```

Maybe related to https://github.com/HelloZeroNet/ZeroNet/issues/1056

Review the installation guidance alongside requirements.txt and the startup path in zeronet.py and src/main.py. Check issue 1056 for related context and reproduce the reported dependency failure if possible. Done means the installation instructions clearly cover the required setup and the reported startup problem is addressed or explained.

Written by the indexing model from the issue text.