Update docs

Author: odarriba

guides/Getting Started.md

@@ -106,6 +106,8 @@ The `ErrorTracker.set_context/1` function stores the given context in the curren
 ErrorTracker.set_context(%{user_id: conn.assigns.current_user.id})
 ```
 
+There are some requirements on the type of data that can be included in the context, so we recommend taking a look at `set_context/1` documentation
+
 ## Manual error tracking
 
 If you want to report custom errors that fall outside the default integration scope, you may use `ErrorTracker.report/2`. This allows you to report an exception yourself:

lib/error_tracker.ex

@@ -41,6 +41,9 @@ defmodule ErrorTracker do
   can gather, but aside from that, you can also add your own information. You can
   do this in a per-process basis or in a per-call basis (or both).
 
+  There are some requirements on the type of data that can be included in the
+  context, so we recommend taking a look at `set_context/1` documentation.
+
   **Per process**
 
   This allows you to set a general context for the current process such as a Phoenix
@@ -152,6 +155,17 @@ defmodule ErrorTracker do
 
   That means that any existing data on deep levels for he current context will
   be replaced if the first level key is received on the new contents.
+
+  ## Content serialization
+
+  The content stored on the context should be serializable using the JSON library
+  used by the application (usually `Jason`), so it is rather recommended to use
+  primitive types (strings, numbers, booleans...).
+
+  If you still need to pass more complex data types to your context, please test
+  that they can be encoded to JSON or storing the errors will fail. In the case
+  of `Jason` that may require defining an Encoder for that data type if not
+  included by default.
   """
   @spec set_context(context()) :: context()
   def set_context(params) when is_map(params) do