minor #12035 info about JWT token generation required (rafbit)

This PR was merged into the 1.9-dev branch.

Discussion
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Added info about JWT token generation required to use API.

| Q               | A
| --------------- | -----
| Branch?         | 1.8 and master
| Bug fix?        | no
| New feature?    | no
| BC breaks?      | no
| Deprecations?   | no
| Related tickets | no
| License         | MIT




Commits
-------

c45b1d9 info about JWT token generation required
f30e873 Update docs/api/index.rst

docs/api/index.rst

@@ -9,6 +9,8 @@ Unified API
     The new, unified Sylius API is still under development, that's why the whole ``ApiBundle`` is tagged with ``@experimental``.
     This means that all code from ``ApiBundle`` is excluded from :doc:`Backward Compatibility Promise </book/organization/backward-compatibility-promise>`.
 
+To use this API remember to generate JWT token. For more information, please visit [jwt package documentation](https://github.com/lexik/LexikJWTAuthenticationBundle/blob/master/Resources/doc/index.md#generate-the-ssh-keys)
+
 This part of the documentation is about the currently developed unified API for the Sylius platform.
 
 .. toctree::