Improve language in git-merge.txt and related docs

Improve some minor language and format issues like hyphenation,
phrases, spacing, word order, comma, attributes.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/Documentation/git-merge-tree.txt b/Documentation/git-merge-tree.txt
index dbb0c18..f869a7f 100644
--- a/Documentation/git-merge-tree.txt
+++ b/Documentation/git-merge-tree.txt
@@ -14,14 +14,14 @@
 -----------
 Reads three treeish, and output trivial merge results and
 conflicting stages to the standard output.  This is similar to
-what three-way read-tree -m does, but instead of storing the
+what three-way 'git read-tree -m' does, but instead of storing the
 results in the index, the command outputs the entries to the
 standard output.
 
 This is meant to be used by higher level scripts to compute
-merge results outside index, and stuff the results back into the
+merge results outside of the index, and stuff the results back into the
 index.  For this reason, the output from the command omits
-entries that match <branch1> tree.
+entries that match the <branch1> tree.
 
 Author
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