docs: crypto: descore-readme.txt: convert to ReST format

Convert this readme file to ReST file format, preserving its
contents as-is as much as possible. The only changes are:

- Added chapter and title markups;
- Added blank lines where needed;
- Added list markups where needed;
- Use a table markup;
- replace markups like `foo' to ``foo``;
- add one extra literal markup to avoid warnings.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/1426be1c7758c0224418352665040220b8a31799.1592203650.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>