added templates and enhanced readme (#307)

Co-authored-by: Justin Lee <justinai@fb.com>

.github/ISSUE_TEMPLATE/feature-request.yml

@@ -0,0 +1,31 @@
+name: 🚀 Feature request
+description: Submit a proposal/request for a new llama-stack feature
+
+body:
+- type: textarea
+  id: feature-pitch
+  attributes:
+    label: 🚀 The feature, motivation and pitch
+    description: >
+      A clear and concise description of the feature proposal. Please outline the motivation for the proposal. Is your feature request related to a specific problem? e.g., *"I'm working on X and would like Y to be possible"*. If this is related to another GitHub issue, please link here too.
+  validations:
+    required: true
+
+- type: textarea
+  id: alternatives
+  attributes:
+    label: Alternatives
+    description: >
+      A description of any alternative solutions or features you've considered, if any.
+
+- type: textarea
+  id: additional-context
+  attributes:
+    label: Additional context
+    description: >
+      Add any other context or screenshots about the feature request.
+
+- type: markdown
+  attributes:
+    value: >
+      Thanks for contributing 🎉!