Clarify the differences between all the file APIs.

[ChaituVR]

Closes ipfs/ipfs-docs#301

As mentioned in https://discuss.ipfs.io/t/why-is-ipfs-files-ls-being-deprecated/7881/9

• Clarify that ipfs file ls is being
  • Why it's being deprecated.
  • Users should use ipfs ls instead.
• Explain that ipfs ls works on IPFS paths, and ipfs files ls works on both IPFS paths and MFS paths.

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[ChaituVR]

Thanks @Stebalien, Changed a few things, Please review again and let me know if something can be improved

[ChaituVR]

@Stebalien Changed a few things, now only ipfs files ls command have

ipfs files ls works on both IPFS paths and MFS paths.

so for someone looking for MFS paths can find this helpful, and new users may just ignore it has IPFS mentioned

[aschmahmann]

Thanks @Stebalien and @ChaituVR