Fix typo in xml_tools TODO and update CONTRIBUTING.md (#343)

Low-hanging PR to start contributing to this project.  

### Key Changes

- Fix typo in TODO comment in `rigging/transform/xml_tools.py` (cased →
cases).
- Update CONTRIBUTING.md: remove the CLA step from the PR guidelines and
the Facebook CLA section. Not sure but I was reading the contributing
guidelines and this section seemed a bit off -- since it refers to
Facebook’s CLA and this repo is clearly not one, so it doesn’t seem to
apply here -- removed for now; maintainers can add a dreadnode-specific
CLA link if needed. Apologies if I misunderstood it.

### Added

- (none)

### Changed

- **rigging/transform/xml_tools.py:** TODO comment now reads “handle
cases where…”.
- **.github/CONTRIBUTING.md:** Removed the Contributor License Agreement
bullet from the PR guidelines and the Facebook CLA section.

### Removed

- References to Facebook and the code.facebook.com CLA from
CONTRIBUTING.md.

Author: GangGreenTemperTatum

.github/CONTRIBUTING.md

@@ -12,7 +12,6 @@ We actively welcome your pull requests.
 3. If you've changed APIs, update the documentation.
 4. Ensure the test suite passes.
 5. Make sure your code lints.
-6. If you haven't already, complete the Contributor License Agreement ("CLA").
 
 ### PR Description Format
 
@@ -54,13 +53,6 @@ Example:
 - Deprecated setup scripts
 ```
 
-## Contributor License Agreement ("CLA")
-
-In order to accept your pull request, we need you to submit a CLA. You only need
-to do this once to work on any of Facebook's open source projects.
-
-Complete your CLA here: <https://code.facebook.com/cla>
-
 ## Issues
 
 We use GitHub issues to track public bugs. Please ensure your description is

rigging/transform/xml_tools.py

@@ -373,7 +373,7 @@ async def xml_to_tools_transform(chat: "Chat") -> "Chat":  # noqa: PLR0912
                 message.remove_slices(XmlToolCall)
 
             # Convert our tool responses
-            # TODO: handle cased where multiple tool responses are present
+            # TODO: handle cases where multiple tool responses are present
 
             for message in chat.all:
                 if (tool_response := message.try_parse(ToolResponse)) is None: