add type hints to media linker code samples

Author: ssteinbach

docs/tutorials/write-a-media-linker.md

@@ -4,9 +4,11 @@ OpenTimelineIO Media Linkers are plugins that allow OTIO to replace MissingRefer
 
 The current MediaLinker can be specified as an argument to `otio.adapters.read_from_file` or via an environment variable.  If one is specified, then it will run after the adapter reads the contents of the file before it is returned back.
 
+```python
     #/usr/bin/env python
     import opentimelineio as otio
     mytimeline = otio.adapters.read_from_file("something.edl", media_linker_name="awesome_studios_media_linker")
+```
 
 After the EDL adapter reads something.edl, the media linker "awesome_studios_media_linker" will run and link the media in the file (if it can).
 
@@ -16,25 +18,28 @@ After the EDL adapter reads something.edl, the media linker "awesome_studios_med
 To create a new OTIO Adapter, you need to create a file mymedialinker.py. Then add a manifest that points at that python file:
 
 
+```json
         {
             "OTIO_SCHEMA" : "PluginManifest.1",
             "media_linkers" : [
                 {
                     "OTIO_SCHEMA" : "MediaLinker.1",
                     "name" : "awesome_studios_media_linker",
-                    "execution_scope" : "in process",
                     "filepath" : "mymedialinker.py"
                  }
             ],
             "adapters" : [
             ]
         }
+```
           
 Then you need to add this manifest to your `$OTIO_PLUGIN_MANIFEST_PATH` environment variable (which is separated with `:` for POSIX or `;` for Windows).
 
 Finally, to specify this linker as the default media linker, set `OTIO_DEFAULT_MEDIA_LINKER` to the name of the media linker:
 
-    setenv OTIO_DEFAULT_MEDIA_LINKER "awesome_studios_media_linker"
+```bash
+    export OTIO_DEFAULT_MEDIA_LINKER="awesome_studios_media_linker"
+```
 
 To package and share your media linker, follow [these instructions](write-an-adapter.md#packaging-and-sharing-custom-adapters).
 
@@ -44,17 +49,20 @@ To write a media linker, write a python file with a "link_media_reference" funct
 
 For example:
 
+```python
     def link_media_reference(in_clip, media_linker_argument_map):
         d.update(media_linker_argument_map)
         # you'll probably want to set it to something other than a missing reference
         in_clip.media_reference = otio.schema.MissingReference(
             name=in_clip.name + "_tweaked",
             metadata=d
         )
+```
 
 ## For Testing
 
 The otioconvert.py script has a --media-linker argument you can use to test out your media linker (once its on the path).
 
+```bash
     env OTIO_PLUGIN_MANIFEST_PATH=mymanifest.otio.json:$OTIO_PLUGIN_MANIFEST_PATH bin/otioconvert.py -i somefile.edl --media-linker="awesome_studios_media_linker" -o /var/tmp/test.otio
-
+```