git-commit-graph.txt: refer to "*commit*-graph file"

This document sometimes refers to the "commit-graph file" as just "the
graph file". This saves a couple of words here and there at the risk of
confusion. In particular, the documentation for `git commit-graph read`
appears to suggest that there are indeed different types of graph files.

Let's just write out the full name everywhere.

The full name, by the way, is not the dash-less "commit graph file".
Use the dashed form. (The next commit will fix the remaining few
instances of the "commit graph file" in this document.)

Signed-off-by: Martin Ågren <[email protected]>
Reviewed-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: Martin Ågren

Documentation/git-commit-graph.txt

@@ -54,8 +54,8 @@ existing commit-graph file.
 
 'read'::
 
-Read a graph file given by the commit-graph file and output basic
-details about the graph file. Used for debugging purposes.
+Read the commit-graph file and output basic details about it.
+Used for debugging purposes.
 
 'verify'::
 
@@ -73,20 +73,20 @@ EXAMPLES
 $ git commit-graph write
 ------------------------------------------------
 
-* Write a graph file, extending the current graph file using commits
-  in `<pack-index>`.
+* Write a commit-graph file, extending the current commit-graph file
+  using commits in `<pack-index>`.
 +
 ------------------------------------------------
 $ echo <pack-index> | git commit-graph write --stdin-packs
 ------------------------------------------------
 
-* Write a graph file containing all reachable commits.
+* Write a commit-graph file containing all reachable commits.
 +
 ------------------------------------------------
 $ git show-ref -s | git commit-graph write --stdin-commits
 ------------------------------------------------
 
-* Write a graph file containing all commits in the current
+* Write a commit-graph file containing all commits in the current
   commit-graph file along with those reachable from `HEAD`.
 +
 ------------------------------------------------