Add some information on x265 settings

[jcj83429]

I did a bunch of test encodes and found some good x265 settings that can beat x264 consistently even for film content at high-ish bitrates and grainy content. Some of the settings I found were surprising (like --rdoq-level 0) as they involve disabling features enabled by higher presets. I added detailed explanations for each flag.

[Simulp]

Looks good, unfortunately since I don't have a lot of experience with x265, I can't comment on any of the suggestions. Though one thing I do know is: Please use lossless WebP for the comparisons.

cwebp -mt -lossless -z 9 -alpha_filter best -metadata icc [input] -o [output]

[jcj83429]

Incorporated community feedback

• No longer recommend --rdoq-level 0 as a general purpose option. At high bitrates it's worse than the default. Instead, moved it to a separate section of "interesting" settings.
• Removed --deblock -3:-3. Since the default RDOQ settings produce more sharpness and roughness than the source, a little more deblock doesn't hurt. For --rdoq-level 0 encodes at lower bitrates, deblock helps reduce twitchiness.

[gianni-rosato]

LGTM, but I'm not very well versed on x265 knowledge. @Simulping IDK if you have already, but if you could get Lyra involved that'd be great