s3: allow anonymous access to public repositories - fixes #154

When setting up the remote, leave both the access key and secret key
blank.

docs/content/s3.md

@@ -133,6 +133,44 @@ created in.  If you attempt to access a bucket from the wrong region,
 you will get an error, `incorrect region, the bucket is not in 'XXX'
 region`.
 
+### Anonymous access to public buckets ###
+
+If you want to use rclone to access a public bucket, configure with a
+blank `access_key_id` and `secret_access_key`.  Eg
+
+```
+e) Edit existing remote
+n) New remote
+d) Delete remote
+q) Quit config
+e/n/d/q> n
+name> anons3
+What type of source is it?
+Choose a number from below
+ 1) amazon cloud drive
+ 2) drive
+ 3) dropbox
+ 4) google cloud storage
+ 5) local
+ 6) s3
+ 7) swift
+type> 6
+AWS Access Key ID - leave blank for anonymous access.
+access_key_id> 
+AWS Secret Access Key (password) - leave blank for anonymous access.
+secret_access_key> 
+Region to connect to.
+region> 1
+endpoint> 
+location_constraint> 
+```
+
+Then use it as normal with the name of the public bucket, eg
+
+    rclone lsd anons3:1000genomes
+
+You will be able to list and copy data but not upload it.
+
 ### Ceph ###
 
 Ceph is an object storage system which presents an Amazon S3 interface.