docs(thumbnails): mention processors in readme

services/thumbnails/README.md

@@ -10,9 +10,9 @@ The relevant environment variables defining file locations are:
 -   (2) `STORAGE_USERS_OCIS_ROOT`
 -   (3) `THUMBNAILS_FILESYSTEMSTORAGE_ROOT`
 
-(1) ... Having a default set by the Infinite Scale code, but if defined, used as base path for other services.  
-(2) ... Source files, defaults to (1) plus path component, but can be freely defined if required.  
-(3) ... Target files, defaults to (1) plus path component, but can be freely defined if required.  
+(1) ... Having a default set by the Infinite Scale code, but if defined, used as base path for other services.
+(2) ... Source files, defaults to (1) plus path component, but can be freely defined if required.
+(3) ... Target files, defaults to (1) plus path component, but can be freely defined if required.
 
 For details and defaults for these environment variables see the ocis admin documentation.
 
@@ -45,9 +45,20 @@ Various resolutions can be defined via `THUMBNAILS_RESOLUTIONS`. A requestor can
 
 Example:
 
-Requested: 18x12  
-Available: 30x20, 15x10, 9x6  
-Returned: 15x10  
+Requested: 18x12
+Available: 30x20, 15x10, 9x6
+Returned: 15x10
+
+## Thumbnail Processors
+
+Image generation can be configured by defining different processors, following processors are available:
+
+* resize
+* fit
+* fill
+* thumbnail
+
+to apply one of those, a query parameter has to be added to the request, e.g. `?processor=fit`
 
 ## Deleting Thumbnails