Update README.md: Suggestions for REST API

Changelog:
-When creating a computer, changed "POST /computers" to "POST /computer" (we are only adding one entity)
-In GET /computers query parameters, "filter" should be applied to either the computer or the company name. i.e.: "Apple" should fetch all computers from the company Apple Inc, plus those who have "Apple" in their name.
-In GET /computers query parameters, "orderBy": precised "computer name" for default value instead of "name" (could be mixed up with "company name")
Update README.md

Changelog:
-Reverted changes for computer creation
-Changed Response 400 comment
Merge pull request #1 from loicortola/master

Update README.md: Suggestions for REST API