Update README to reference baseBranch, use "main" as default in examples (#180)

* chore(docs): Update README to reference baseBranch

- Adds reference to the `baseBranch` config in the Changesets docs
- Updates all references in examples to `main` instead of `master`
  - `main` is now the default branch in new GitHub projects
  - This change aligns with the comment in the `baseBranch` section of Changesets docs

* remove commit sha from docs URL

README.md

@@ -1,6 +1,6 @@
 # Changesets Release Action
 
-This action for [Changesets](https://github.com/atlassian/changesets) creates a pull request with all of the package versions updated and changelogs updated and when there are new changesets on master, the PR will be updated. When you're ready, you can merge the pull request and you can either publish the packages to npm manually or setup the action to do it for you.
+This action for [Changesets](https://github.com/atlassian/changesets) creates a pull request with all of the package versions updated and changelogs updated and when there are new changesets on [your configured `baseBranch`](https://github.com/changesets/changesets/blob/main/docs/config-file-options.md#basebranch-git-branch-name), the PR will be updated. When you're ready, you can merge the pull request and you can either publish the packages to npm manually or setup the action to do it for you.
 
 ## Usage
 
@@ -31,7 +31,7 @@ name: Release
 on:
   push:
     branches:
-      - master
+      - main
 
 concurrency: ${{ github.workflow }}-${{ github.ref }}
 
@@ -67,7 +67,7 @@ name: Release
 on:
   push:
     branches:
-      - master
+      - main
 
 concurrency: ${{ github.workflow }}-${{ github.ref }}
 
@@ -134,7 +134,7 @@ name: Release
 on:
   push:
     branches:
-      - master
+      - main
 
 jobs:
   release:
@@ -176,7 +176,7 @@ name: Release
 on:
   push:
     branches:
-      - master
+      - main
 
 concurrency: ${{ github.workflow }}-${{ github.ref }}