Fix broken link.

PiperOrigin-RevId: 260548004

Renaming doc files to make the file names more palatable and in preparation for including documentation in sync process

Rename AdvancedGuide.md to advanced.md and adjust the links. 
Part of documentation rationalization work

Add a hyphen to 'ad hoc' and change 'distance' to plural.

Put occurrences of "#include" in a code span so they are not interpreted
as headers.

Other documents were not broken because the #include was not at the
start of the line, but put them in code spans anyway just in case the
text gets refilled in the future.