Update for FIPS documentation (#1610)

### Issues:
Resolves: CryptoAlg-2419

### Description of changes: 
Updating the documentation about our FIPS module.
* You can see the markdown rendered here:
https://github.com/justsmth/aws-lc/blob/fips-doc-update/crypto/fipsmodule/FIPS.md

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under the terms of the Apache 2.0 license and the ISC license.