fix: fix sphinx documentation

All documentation must be in doc directory to allow sphinx to correctly
generate it, so move all documentation in doc instead of adding links
from doc to upper directories

While at it, also fix other sphinx errors/issues:
 - README.html -> README.md
 - yml -> yaml
 - csv -> text
 - html -> jinja
 - Remove ... from json
 - Remove ---------------------- from markdown
 - Use local links instead of https://github.com/ossf/cve-bin-tool (it
   is portable and works both with markdown and sphinx)

Signed-off-by: Fabrice Fontaine <[email protected]>

Author: ffontaine

CONTRIBUTING.md

@@ -0,0 +1 @@
+doc/CONTRIBUTING.md

CONTRIBUTING.md

@@ -0,0 +1 @@
+doc/README.md

README.md

@@ -0,0 +1 @@
+../../doc/checkers/README.md

README.md

@@ -0,0 +1 @@
+../../doc/parsers/README.md

cve_bin_tool/checkers/README.md

@@ -1 +1 @@
-../cve_bin_tool/checkers/README.md
+checkers/README.md