Add gjo (#2406)

Please check if what you want to add to `awesome-go` list meets [quality standards](https://github.com/avelino/awesome-go/blob/master/CONTRIBUTING.md#quality-standard) before sending pull request. Thanks!

**Please provide package links to:**

- github.com repo:https://github.com/skanehira/gjo
- godoc.org:https://godoc.org/github.com/skanehira/gjo
- goreportcard.com:https://goreportcard.com/report/github.com/skanehira/gjo
- coverage service link [gocover](https://gocover.io/github.com/skanehira/gjo)


Very good coverage

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- [x] I have added my package in alphabetical order.
- [x] I have an appropriate description with correct grammar.
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Thanks for your PR, you're awesome! 👍

README.md

@@ -829,6 +829,7 @@ See [go-hardware](https://github.com/rakyll/go-hardware) for a comprehensive lis
 
 *Libraries for working with JSON.*
 
+* [gjo](https://github.com/skanehira/gjo) - Small utility to create JSON objects.
 * [GJSON](https://github.com/tidwall/gjson) - Get a JSON value with one line of code.
 * [go-respond](https://github.com/nicklaw5/go-respond) - Go package for handling common HTTP JSON responses.
 * [gojq](https://github.com/elgs/gojq) - JSON query in Golang.