add a release checklist

Currently this list isn't publicly available, it sits in various
different versions on @damiendoligez's filesystems. He sent me a copy
when I took care of some of the recent releases. The present
presentation is a result of significant cleanups and changes to the
checklist -- in particular, some mistakes may have jumped in.

This is not a scripted process, it is very informal and it is likely
that there are some mistakes/omissions in the list. Yet, it sounds
better to have it somewhere in the source repository than not have it
around at all. It was certainly helpful to me, and it probably would
be to other release-help volunteers.

(The list is put in tools/ because there isn't a clearly better place
for it. This choice was suggested by Damien.)

.gitattributes

@@ -51,7 +51,7 @@ README*                  ocaml-typo=missing-header
 # dra27 too lazy to update check-typo to interpret Cmd-style comments!
 /tools/ci/appveyor/appveyor_build.cmd      ocaml-typo=long-line,very-long-line,missing-header,non-ascii text eol=crlf
 /tools/ci/appveyor/appveyor_build.sh       ocaml-typo=non-ascii
-
+/tools/release-checklist                   ocaml-typo=missing-header
 
 asmcomp/*/emit.mlp       ocaml-typo=tab,long-line,unused-prop
 asmcomp/power/NOTES.md   ocaml-typo=missing-header

Changes

@@ -185,6 +185,10 @@ Working version
 - GPR#1833: allow non-val payloads in CMM Ccatch handlers
   (Simon Fowler, review by Xavier Clerc)
 
+- GPR#1877: document the release process
+  (Damien Doligez and Gabriel Scherer, review by Sébastien Hinderer,
+   Perry E. Metzger, Xavier Leroy and David Allsopp)
+
 - GPR#1886: move the Location.absname reference to Clflags.absname
   (Armaël Guéneau, review by Jérémie Dimino)