docs: revert oasdiff.yaml configuration section (#113)

The documented path (oasdiff.yaml at the repo root) is unconventional
for a CI/lint tool. Most tools in this category use a dotfile
convention (.eslintrc, .prettierrc, .golangci.yml, .yamllint, etc.).

Pulling the section so customers don't adopt the unconventional path
and have to migrate later. The CLI lookup will move to .oasdiff.* in
a follow-up; documentation will return at that point with the right
path.

Keeps the rest of the README intact: the TOC structure (only the line
for this removed section is dropped), the boolean-limitation wording
fix from #111, all action subsections.

Author: reuvenharrison

README.md

@@ -10,7 +10,6 @@ GitHub Actions for comparing OpenAPI specs and detecting breaking changes, based
   - [Check for breaking changes](#check-for-breaking-changes)
   - [Generate a changelog](#generate-a-changelog)
   - [Generate a diff report](#generate-a-diff-report)
-  - [Configuring with `oasdiff.yaml`](#configuring-with-oasdiffyaml)
 - [Spec paths](#spec-paths)
 - [Pro: Rich PR comment](#pro-rich-pr-comment)
 
@@ -156,25 +155,6 @@ jobs:
 | `flatten-allof` | `false` | Merge allOf subschemas into a single schema before diff | `true`, `false` |
 | `output-to-file` | `''` | Write output to this file path instead of stdout | file path |
 
-### Configuring with `oasdiff.yaml`
-
-All free actions inherit the CLI's config-file support. Drop an `oasdiff.yaml` at your repo root and the actions pick it up automatically — no extra wiring needed:
-
-```yaml
-# oasdiff.yaml at your repo root
-exclude-elements:
-  - endpoints
-flatten-allof: true
-deprecation-days-stable: 180
-fail-on: ERR
-```
-
-Any flag the oasdiff CLI supports works in the config file — see [CONFIG-FILES.md](https://github.com/oasdiff/oasdiff/blob/main/docs/CONFIG-FILES.md) for the full reference and supported file formats (`oasdiff.{json,yaml,yml,toml,hcl}`).
-
-Action `inputs:` take precedence over config-file values, so you can use the file for shared defaults across workflows and override per-workflow via inputs.
-
-> **Limitation**: action inputs can only turn a boolean flag *on*, not *off*. If your `oasdiff.yaml` sets `composed: true`, passing `composed: 'false'` to the action has no effect — to disable it for a specific workflow run, edit the YAML.
-
 ---
 
 ## Spec paths