Adds docs for parallelism

Integrates PR feedback from users as well. This will be supported in
subsequent commits.

README.md

@@ -144,7 +144,7 @@ but realized that it has a wide array of applications and decided to release it
 
 While Burr is stable and well-tested, we have quite a few tools/features on our roadmap!
 
-1. Parallelism -- support for recursive "sub-agents" through an ergonomic API (not: this is already feasible, see [recursive applications](http://localhost:8000/concepts/recursion/)).
+1. Parallelism -- support for recursive "sub-agents" through an ergonomic API (not: this is already feasible, see [recursive applications](https://burr.dagworks.io/recursion/)).
 2. Testing & eval curation. Curating data with annotations and being able to export these annotations to create unit & integration tests.
 3. Various efficiency/usability improvements for the core library (see [planned capabilities](https://burr.dagworks.io/concepts/planned-capabilities/) for more details). This includes:
    1. First-class support for retries + exception management

docs/_static/custom.css

@@ -0,0 +1,5 @@
+/* Enable line wrapping for code blocks */
+.highlight pre {
+  white-space: pre-wrap;
+  word-wrap: break-word;
+}

docs/concepts/index.rst

@@ -21,5 +21,6 @@ Overview of the concepts -- read these to get a mental model for how Burr works.
     state-typing
     hooks
     additional-visibility
+    parallelism
     recursion
     planned-capabilities