feat: sync docs with main chartmuseum repo

[cbuto]

Related to #9

For the most part this was copying the existing docs from https://github.com/helm/chartmuseum but I did take the opportunity to make some small adjustments! Let me know what you think

1. I changed the background and text colors for code blocks, I had a hard time reading the dark blue text on the black background. The CSS changes make code blocks use white text with a black-ish background:

If we want to stick with the dark blue, that's totally cool!

2. I changed the Other CLI Options page to be All CLI Options. I was going to add some new CLI options to that existing page but it wasn't super easy to figure out what wasn't mentioned previously and get it formatted correctly. I just grabbed the output from chartmuseum -h and listed all the options. This will probably be easier to maintain down the line as well!

[jdolitsky]

This is incredible! Thanks so much @cbuto