Add Strapi headless CMS

[ghostpirate]

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• Your submissions are formatted according to the following requirements:

- [Name](http://homepage/) - Short description, less than 250 characters. ([Demo](http://url.to/demo), [Source Code](http://url.of/source/code), [Clients](https://url.to/list/of/related/clients-or-apps)) `License` `Language`

Depends on proprietary services:

- [Name](http://homepage/) `⚠` - Short description, less than 250 characters. ([Demo](http://url.to/demo), [Source Code](http://url.of/source/code), [Clients](https://url.to/list/of/related/clients-or-apps)) `License` `Language`

Non-free software in non-free.md:

- [Name](http://homepage/) `⊘ Proprietary` - Short description, less than 250 characters. ([Demo](http://url.to/demo), [Source Code](http://url.of/source/code), [Clients](https://url.to/list/of/related/clients-or-apps)) `Language`

• Your additions are ordered alphabetically.
• Your additions are Free software, or if not they have been added to non-free and marked ⊘ Proprietary.
• If your additions depend on proprietary services outside the user's control, they must be marked ⚠.
• Your additions are not already listed at awesome-sysadmin (IT infrastructure management), staticgen.com or staticsitegenerators.net (static site generators).
• Your additions have their License main server-side Language/platform/requirement listed.
• Any licenses you have added are in our list of licenses.
• You have searched the repository for any relevant issues or PRs, incluing closed ones.
• If the main link of your addition points to the program's source code, there is no need to add a duplicate Source Code link. The Demo and Clients links are not mandatory.
• Any category you are creating has the minimum requirement of 3 items. If not, your addition may be inserted into Misc/Other.
• Any software project you are adding to the list is actively maintained.