accidentally not enabling `conda init` on installation

### Comment:

mamba is awesome. thank you for this great software.

I just installed from mambaforge as per:
https://github.com/conda-forge/miniforge#mambaforge

and accidentally hit enter while waiting for the installation such that it "no" before i realised what happened. i wanted to hit "yes".


I then spent the next 20mins trying to figure out what to put in the `.bashrc` file to allow for the `conda init`.
Didn't get anywhere so in the end deleted my wsl distro and started again from scratch. the whole experience was pretty annoying.

Suggestions:

1. don't default to "no" in the CLI. default to nothing and require the user to choose. give guidance as required.
2. in the docs tell the user what to add to the `.bashrc` file to reproduce what hitting "yes" does, i.e. `` is path to mambaforge root installation
```
# >>> conda initialize >>>
# !! Contents within this block are managed by 'conda init' !!
__conda_setup="$('/mambaforge/bin/conda' 'shell.bash' 'hook' 2> /dev/null)"
if [ $? -eq 0 ]; then
eval "$__conda_setup"
else
if [ -f "/mambaforge/etc/profile.d/conda.sh" ]; then
. "/mambaforge/etc/profile.d/conda.sh"
else
export PATH="/mambaforge/bin:$PATH"
fi
fi
unset __conda_setup

if [ -f "/mambaforge/etc/profile.d/mamba.sh" ]; then
. "/mambaforge/etc/profile.d/mamba.sh"
fi
# <<< conda initialize <<<
```