chore(ci): correct the direction of diff equations (#2396)

### Updates to .github/actions/file-diff
- path renamed to head-path
- diff-path renamed to base-path
- this same renaming is carried throughout the file-diff/index.js file
- before the summary table, I added a clarifying note
- fixed the summary table to report on changes to the main file
- more comments throughout

Author: castastrophe

.github/actions/file-diff/README.md

@@ -4,11 +4,11 @@ A GitHub Action for comparing compiled assets between branches.
 
 ## Inputs
 
-### `path`
+### `head-path`
 
 **Required** Path to file or directory for file sizes analysis.
 
-### `diff-path`
+### `base-path`
 
 **Optional** Path to another directory against which to perform file comparisons.
 
@@ -44,8 +44,8 @@ Total size of all files for this branch in bytes.
 name: Compare compiled output file size
 uses: "spectrum-tools/gh-action-file-diff"
 with:
-    path: ${{ github.workspace }}/pull-request
-    diff-path: ${{ github.workspace }}/base-branch
+    head-path: ${{ github.workspace }}/pull-request
+    base-path: ${{ github.workspace }}/base-branch
     file-glob-pattern: |
         components/*/dist/*.{css,json}
         components/*/dist/themes/*.css

.github/actions/file-diff/action.yml

@@ -2,11 +2,11 @@ name: "File comparisons"
 description: "Compares files between branches."
 author: "spectrum-tools"
 inputs:
-    path:
+    head-path:
         description: "Path to file or directory for file sizes analysis."
         required: false
         default: ${{ github.workspace }}
-    diff-path:
+    base-path:
         description: "Optional path to another directory to perform file size diff against the provided path."
         required: false
     token: