s3: add docs on how to add a new provider

CONTRIBUTING.md

@@ -484,6 +484,46 @@ alphabetical order of full name of remote (e.g. `drive` is ordered as
 Once you've written the docs, run `make serve` and check they look OK
 in the web browser and the links (internal and external) all work.
 
+## Adding a new s3 provider
+
+It is quite easy to add a new S3 provider to rclone.
+
+You'll need to modify the following files
+
+- `backend/s3/s3.go`
+    - Add the provider to `providerOption` at the top of the file
+    - Add endpoints and other config for your provider gated on the provider in `fs.RegInfo`.
+    - Exclude your provider from genric config questions (eg `region` and `endpoint).
+    - Add the provider to the `setQuirks` function - see the documentation there.
+- `docs/content/s3.md`
+    - Add the provider at the top of the page.
+    - Add a section about the provider linked from there.
+    - Add a transcript of a trial `rclone config` session
+        - Edit the transcript to remove things which might change in subsequent versions
+    - **Do not** alter or add to the autogenerated parts of `s3.md`
+    - **Do not** run `make backenddocs` or `bin/make_backend_docs.py s3`
+- `README.md` - this is the home page in github
+    - Add the provider and a link to the section you wrote in `docs/contents/s3.md`
+- `docs/content/_index.md` - this is the home page of rclone.org
+    - Add the provider and a link to the section you wrote in `docs/contents/s3.md`
+
+When adding the provider, endpoints, quirks, docs etc keep them in
+alphabetical order by `Provider` name, but with `AWS` first and
+`Other` last.
+
+Once you've written the docs, run `make serve` and check they look OK
+in the web browser and the links (internal and external) all work.
+
+Once you've written the code, test `rclone config` works to your
+satisfaction, and check the integration tests work `go test -v -remote
+NewS3Provider:`. You may need to adjust the quirks to get them to
+pass. Some providers just can't pass the tests with control characters
+in the names so if these fail and the provider doesn't support
+`urlEncodeListings` in the quirks then ignore them. Note that the
+`SetTier` test may also fail on non AWS providers.
+
+For an example of adding an s3 provider see [eb3082a1](https://github.com/rclone/rclone/commit/eb3082a1ebdb76d5625f14cedec3f5154a5e7b10).
+
 ## Writing a plugin ##
 
 New features (backends, commands) can also be added "out-of-tree", through Go plugins.

backend/s3/s3.go

@@ -70,6 +70,9 @@ import (
 // NB if you add a new provider here, then add it in the setQuirks
 // function and set the correct quirks. Test the quirks are correct by
 // running the integration tests "go test -v -remote NewS3Provider:".
+//
+// See https://github.com/rclone/rclone/blob/master/CONTRIBUTING.md#adding-a-new-s3-provider
+// for full information about how to add a new s3 provider.
 var providerOption = fs.Option{
 	Name: fs.ConfigProvider,
 	Help: "Choose your S3 provider.",
@@ -2998,15 +3001,17 @@ func setEndpointValueForIDriveE2(m configmap.Mapper) (err error) {
 // There should be no testing against opt.Provider anywhere in the
 // code except in here to localise the setting of the quirks.
 //
-// These should be differences from AWS S3
+// Run the integration tests to check you have the quirks correct.
+//
+//	go test -v -remote NewS3Provider:
 func setQuirks(opt *Options) {
 	var (
-		listObjectsV2         = true
-		virtualHostStyle      = true
-		urlEncodeListings     = true
-		useMultipartEtag      = true
-		useAcceptEncodingGzip = true
-		mightGzip             = true // assume all providers might gzip until proven otherwise
+		listObjectsV2         = true // Always use ListObjectsV2 instead of ListObjects
+		virtualHostStyle      = true // Use bucket.provider.com instead of putting the bucket in the URL
+		urlEncodeListings     = true // URL encode the listings to help with control characters
+		useMultipartEtag      = true // Set if Etags for multpart uploads are compatible with AWS
+		useAcceptEncodingGzip = true // Set Accept-Encoding: gzip
+		mightGzip             = true // assume all providers might use content encoding gzip until proven otherwise
 	)
 	switch opt.Provider {
 	case "AWS":