erofs-utils: improve documentation for upcoming 1.6

Refine README as well as add docs/INSTALL.md and docs/PERFORMANCE.md.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230309112630.74230-2-hsiangkao@linux.alibaba.com
3 files changed