chore(docs): Update RFC template (#35682)

docs/contributing/rfc-process.md

@@ -38,16 +38,22 @@ In short, to get a major feature added to Gatsby, one usually first puts up a Di
 - Copy the RFC template into your clipboard:
 
   ```md
-  # Summary
+  ## Summary
 
   Brief explanation of the feature.
 
-  # Basic example
+  ## Try it out
+
+  Section with instructions on how to use the feature, e.g. with a canary.
+
+  <!-- When defining a canary for installation, tell users to use `--save-exact` (npm) or `--exact` (yarn) flag. -->
+
+  ## Basic example
 
   If the proposal involves a new or changed API, include a basic code example.
   Omit this section if it's not applicable.
 
-  # Motivation
+  ## Motivation
 
   Why are we doing this? What use cases does it support? What is the expected
   outcome?
@@ -57,15 +63,15 @@ In short, to get a major feature added to Gatsby, one usually first puts up a Di
   enumerate the constraints you are trying to solve without coupling them too
   closely to the solution you have in mind.
 
-  # Detailed design
+  ## Detailed design
 
   This is the bulk of the RFC. Explain the design in enough detail for somebody
   familiar with Gatsby to understand, and for somebody familiar with the
   implementation to implement. This should get into specifics and corner-cases,
   and include examples of how the feature is used. Any new terminology should be
   defined here.
 
-  # Drawbacks
+  ## Drawbacks
 
   Why should we _not_ do this? Please consider:
 
@@ -77,17 +83,17 @@ In short, to get a major feature added to Gatsby, one usually first puts up a Di
 
   There are tradeoffs to choosing any path. Attempt to identify them here.
 
-  # Alternatives
+  ## Alternatives
 
   What other designs have been considered? What is the impact of not doing this?
 
-  # Adoption strategy
+  ## Adoption strategy
 
   If we implement this proposal, how will existing Gatsby developers adopt it? Is
   this a breaking change? Can we write a codemod? Should we coordinate with
   other projects or libraries?
 
-  # How we teach this
+  ## How we teach this
 
   What names and terminology work best for these concepts and why? How is this
   idea best presented? As a continuation of existing Gatsby patterns?
@@ -98,7 +104,7 @@ In short, to get a major feature added to Gatsby, one usually first puts up a Di
 
   How should this feature be taught to existing Gatsby developers?
 
-  # Unresolved questions
+  ## Unresolved questions
 
   Optional, but suggested for first drafts. What parts of the design are still
   TBD?