docs/howto/release-git-lfs.md: add RISC-V 64 asset

In PR git-lfs#5438 we added support in our Makefile and scripts to build and
upload a version of our Linux release assets for the RISC-V 64 platform.

As the documentation of our release process includes a list of the
Linux assets we build, we now add an entry for the RISC-V 64 platform
so as to match the assets listed in our public release notes.

docs/howto/release-git-lfs.md

@@ -38,6 +38,7 @@ We package several artifacts for each tagged release. They are:
       | git-lfs-linux-arm64-v@{version}.tar.gz | linux (generic) | arm64 |
       | git-lfs-linux-loong64-v@{version}.tar.gz | linux (generic) | loong64 |
       | git-lfs-linux-ppc64le-v@{version}.tar.gz | linux (generic) | ppc64le |
+      | git-lfs-linux-riscv64-v@{version}.tar.gz | linux (generic) | riscv64 |
       | git-lfs-linux-s390x-v@{version}.tar.gz | linux (generic) | s390x |
 
   2. `git-lfs-windows-v@{release}-@{arch}.zip` for the following values: