docs: sphinxify kcov.txt and move to dev-tools

Another document added to the dev-tools collection.

Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/dev-tools/kcov.rst

@@ -12,19 +12,19 @@ To achieve this goal it does not collect coverage in soft/hard interrupts
 and instrumentation of some inherently non-deterministic parts of kernel is
 disbled (e.g. scheduler, locking).
 
-Usage:
+Usage
-======
+-----
 
-Configure kernel with:
+Configure the kernel with::
 
         CONFIG_KCOV=y
 
 CONFIG_KCOV requires gcc built on revision 231296 or later.
-Profiling data will only become accessible once debugfs has been mounted:
+Profiling data will only become accessible once debugfs has been mounted::
 
         mount -t debugfs none /sys/kernel/debug
 
-The following program demonstrates kcov usage from within a test program:
+The following program demonstrates kcov usage from within a test program::
 
     #include <stdio.h>
     #include <stddef.h>
@@ -85,7 +85,7 @@ int main(int argc, char **argv)
 	return 0;
     }
 
-After piping through addr2line output of the program looks as follows:
+After piping through addr2line output of the program looks as follows::
 
     SyS_read
     fs/read_write.c:562

Documentation/dev-tools/tools.rst

@@ -16,3 +16,4 @@ whole; patches welcome!
 
    coccinelle
    sparse
+   kcov