[doc] Add documentation steps to release process

Following rocq-prover/rocq#21659 ,
rocq-prover/rocq#21661 and
rocq-prover/doc#1

Fixes #239

Author: proux01

dev/doc/howto_release.md

@@ -6,6 +6,10 @@
 * if need be, update supported versions of Rocq in .nix/config.nix
   and regenerate CI config with nix-shell --arg do-nothing true --run "genNixActions"
 * rerun CI
+* run `make refman-html` and push the resulting `_build/default/doc/refman-html`
+  as `vX.Y/refman-stdlib` in https://github.com/rocq-prover/doc/
+* run `make stdlib-html` and push the resulting `_build/default/doc/stdlib/html`
+  as `vX.Y/stdlib` in https://github.com/rocq-prover/doc/
 * release on github (and add the generated tarball as asset)
 * once tagging is done push a commit to update doc/sphinx/changes.rst
   (particularly is_a_released_version)