[DOCS] absent info about install python package python3-redis for redis_cache

[unix196]

Description
In documentation about salt.cache.redis_cache absent info about installing important package:
pip python3-redis
Otherwise in salt master log:

2021-09-20 03:42:04,327 [salt.master      :1879][ERROR   ][39] Error in function _mine:
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/salt/master.py", line 1872, in run_func
    ret = getattr(self, func)(load)
  File "/usr/lib/python3/dist-packages/salt/master.py", line 1441, in _mine
    return self.masterapi._mine(load, skip_verify=True)
  File "/usr/lib/python3/dist-packages/salt/daemons/masterapi.py", line 608, in _mine
    data = self.cache.fetch(cbank, ckey)
  File "/usr/lib/python3/dist-packages/salt/cache/__init__.py", line 180, in fetch
    return self.modules[fun](bank, key, **self._kwargs)
  File "/usr/lib/python3/dist-packages/salt/loader.py", line 1208, in __getitem__
    func = super(LazyLoader, self).__getitem__(item)
  File "/usr/lib/python3/dist-packages/salt/utils/lazy.py", line 108, in __getitem__
    raise KeyError(key)
KeyError: 'redis.fetch'

#57069 - issue with the same problem.

Suggested Fix
For example in doc about etcd_cache:

To enable this cache plugin, the master will need the python client for Etcd installed. This can be easily installed with pip:
pip install python-etcd

Type of documentation
cache modules

Location or format of documentation
https://docs.saltproject.io/en/latest/ref/cache/all/salt.cache.redis_cache.html#module-salt.cache.redis_cache

[waynew]

Thanks for opening the issue - yeah - looks like the documentation should mention that the redis package is needed.

FWIW, if you're interested in opening a PR adding that to the documentation that would be 👍

[unix196]

https://github.com/saltstack/salt/blob/master/doc/ref/cache/all/salt.cache.redis_cache.rst - I found this file, but I don't undestand how edit it.

[barbaricyawps]

Hi, @unix196 . If you're still interested in working on this issue, we would love your help.

To make an edit to the Salt module docs, you first need to set up your environment to contribute in the same way you would set up your environment to contribute to Salt in general. For that reason, it's best to follow the instructions in the Salt Contributing guide: https://github.com/saltstack/salt/blob/master/CONTRIBUTING.rst

Once your environment is good, navigate to the file salt > cache > rediscache.py and edit the docstrings for that module. Hope that helps!