Update B2 docs with Data usage, and Crypt section

docs/content/b2.md

@@ -1,7 +1,7 @@
 ---
 title: "B2"
 description: "Backblaze B2"
-date: "2016-06-15"
+date: "2016-10-25"
 ---
 
 <i class="fa fa-fire"></i>Backblaze B2
@@ -182,6 +182,53 @@ $ rclone -q --b2-versions ls b2:cleanup-test
         9 one.txt
 ```
 
+### Data usage ###
+
+It is useful to know how many requests are sent to the server in different scenarios.
+
+All copy commands send the following 4 requests:
+
+```
+/b2api/v1/b2_authorize_account
+/b2api/v1/b2_create_bucket
+/b2api/v1/b2_list_buckets
+/b2api/v1/b2_list_file_names
+```
+
+The `b2_list_file_names` request will be sent once for every 1k files
+in the remote path, providing the checksum and modification time of
+the listed files. As of version 1.33 issue
+[#818](https://github.com/ncw/rclone/issues/818) causes extra requests
+to be sent when using B2 with Crypt. When a copy operation does not
+require any files to be uploaded, no more requests will be sent.
+
+Uploading files that do not require chunking, will send 2 requests per
+file upload:
+
+```
+/b2api/v1/b2_get_upload_url
+/b2api/v1/b2_upload_file/
+```
+
+Uploading files requiring chunking, will send 2 requests (one each to
+start and finish the upload) and another 2 requests for each chunk:
+
+```
+/b2api/v1/b2_start_large_file
+/b2api/v1/b2_get_upload_part_url
+/b2api/v1/b2_upload_part/
+/b2api/v1/b2_finish_large_file
+```
+
+### B2 with crypt ###
+
+When using B2 with `crypt` files are encrypted into a temporary
+location and streamed from there. This is required to calculate the
+encrypted file's checksum before beginning the upload. On Windows the
+%TMPDIR% environment variable is used as the temporary location. If
+the file requires chunking, both the chunking and encryption will take
+place in memory.
+
 ### Specific options ###
 
 Here are the command line options specific to this cloud storage