docs: add openexr_enable_threading to install.rst cmake options

[nitzan-treg]

hey, saw #2351 — the threading cmake option wasnt listed in the component options section on install.rst so added an entry for it.

kept the wording short and matching the format of the other entries (force_embedded_core, build_testing, etc). verified in cmake/OpenEXRSetup.cmake that the option exists with default ON and is used to gate the threading library lookup.

placed it right after force_embedded_core since both are core library behaviour options.

fixes #2351

[linux-foundation-easycla]

• ❌ - login: @nitzan-treg / name: nitzan-treg . The commit (54efce0) is not authorized under a signed CLA. Please click here to be authorized. For further assistance with EasyCLA, please submit a support request ticket.

[cary-ilm]

This looks great, thanks!

Our project policy requires a signed Contributor License Agreement. Can you click on the red "SIGNED AGREEMENT MISSING" button above and sign the required forms?

Also, we require a Developer Certificate of Origin (DCO), or "signed commits", via commit -s. Can you amend your commit this way:

git commit -s --amend --no-edit
git push --force

That will add the "signed-off-by" statement. It won't work to simply add a second commit because each commit needs the signature, hence the need for the --amend and git push --force.

[cary-ilm]

@nitzan-treg, I'd like to accept this, will you be able to complete the CLA and DCO?

[cary-ilm]

@nitzan-treg, one more try, will you be able to sign the required forms?