docs: Add Contributing Guidelines

[vvatanabe]

Describe the change

• Contributing Guidelines have been added. For details, refer to CONTRIBUTING.md.
• A link to CONTRIBUTING.md has been added in the README.md.
• The Integration Test section from README.md has been moved to CONTRIBUTING.md.
• The outlines for Installation and Usage in README.md have been aligned.

Tests
None

Additional context
None

[codecov]

Codecov Report

Merging #463 (b7b10ac) into master (71a2493) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #463   +/-   ##
=======================================
  Coverage   97.05%   97.05%           
=======================================
  Files          17       17           
  Lines         714      714           
=======================================
  Hits          693      693           
  Misses         15       15           
  Partials        6        6           

[vvatanabe]

@sashabaranov I've written the Contributing Guidelines. Please check them. If there are any rules you'd like to add, remove, or update, please let me know.

[vvatanabe]

@sashabaranov It looks like you're busy, so I'll go ahead and merge this for now. If there are any issues or feedback regarding this guideline, I'll respond right away.

[vvatanabe]

Oh, I see. I can't approve a pull request that I created myself.

[sashabaranov]

This is a really great PR, thank you so much @vvatanabe! Sorry for such a long delay with the review.

Just a note: it seems that golangci-lint does include goimports into itself, so it's enough to run to just run the golangci-lint.

To reproduce:

diff --git a/completion_test.go b/completion_test.go
index 844ef48..3a63504 100644
--- a/completion_test.go
+++ b/completion_test.go
@@ -4,6 +4,7 @@ import (
        . "github.com/sashabaranov/go-openai"
        "github.com/sashabaranov/go-openai/internal/test/checks"

+       "testing"
        "context"
        "encoding/json"
        "errors"
@@ -12,7 +13,6 @@ import (
        "net/http"
        "strconv"
        "strings"
-       "testing"
        "time"
 )

Produces:

% golangci-lint run ./...
completion_test.go:7: File is not `goimports`-ed (goimports)
	"testing"

[vvatanabe]

@sashabaranov Thanks for the feedback. Indeed, golangci-lint does give warnings, but to fix them, you need to run goimports yourself. I've added instructions on how to run goimports to help developers who are not familiar with Go handle it smoothly.

---

Don't worry about the delayed response. You should focus on what you need to prioritize! It's more important.