Tutorial on using JSON with Trigger objects (#9)

docs/trig_json.md

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+# Saving and Loading Trigger Settings from a JSON file
+
+This tutorial will provide an example of saving and subsequently loading a `Trigger` object from a JSON file.
+
+## Initialize Runtime
+
+To start, we'll import `Acquire` and create a `Runtime` object, which coordinates the streaming process.
+
+```python
+import acquire
+runtime = acquire.Runtime()
+```
+
+## Create a Trigger Object
+
+`Trigger` objects have 4 attributes: edge, enable, line, and kind. In this example, will only adjust the edge attribute.
+
+```python
+# Instantiate a Trigger object
+trig = acquire.Trigger()
+
+# change the edge attribute from the default Rising to Falling
+trig.edge = acquire.TriggerEdge.Falling
+```
+
+## Save Properties to a JSON file
+We'll utilize the [json library](https://docs.python.org/3/library/json.html#) to write our `Trigger` to a JSON file to save for subsequent acquisition.
+
+```python
+import json
+
+# cast the properties to a dictionary
+trig = trig.dict()
+
+# convert the dictionary to json with "human-readable" formatting
+trig = json.dumps(trig, indent=4, sort_keys=True)
+
+# save the trigger to file "sample_trig.json" in the current directory
+with open("sample_trig.json", "w") as outfile:
+    outfile.write(trig)
+```
+
+## Example JSON file
+The resulting sample_trig.json file is below:
+
+```json
+{
+    "edge": "Falling",
+    "enable": false,
+    "kind": "Input",
+    "line": 0
+}
+```
+
+## Load Properties from a JSON file
+You can load the trigger attributes in the JSON file to a `Trigger` object as shown below:
+
+```python
+# Instantiate a `Trigger` object from the settings in sample_trig.json
+trig = acquire.Trigger(**json.load(open('sample_trig.json')))
+```
+