diff: update help output to match docs, et al. (#3601)

* diff: update help output to match docs
per https://github.com/iterative/dvc/pull/3566#pullrequestreview-388346350

* terms: git->Git, scm->SCM, spacing

dvc/command/diff.py

@@ -120,9 +120,8 @@ class CmdDiff(CmdBase):
 
 def add_parser(subparsers, parent_parser):
     DIFF_DESCRIPTION = (
-        "Show changes between commits in the DVC repository,"
-        " or between a commit and the workspace. "
-        "Prints the list of paths added, modified, or deleted."
+        "Show added, modified, or deleted data between commits in the DVC"
+        " repository, or between a commit and the workspace."
     )
     diff_parser = subparsers.add_parser(
         "diff",

dvc/command/init.py

@@ -47,7 +47,7 @@ def add_parser(subparsers, parent_parser):
         action="store_true",
         default=False,
         help="Initiate DVC in directory that is "
-        "not tracked by any scm tool (e.g. git).",
+        "not tracked by any SCM tool (e.g. Git).",
     )
     init_parser.add_argument(
         "-f",

dvc/output/base.py

@@ -28,7 +28,7 @@ class OutputIsNotFileOrDirError(DvcException):
 
 class OutputAlreadyTrackedError(DvcException):
     def __init__(self, path):
-        msg = "output '{}' is already tracked by scm (e.g. git)".format(path)
+        msg = "output '{}' is already tracked by SCM (e.g. Git)".format(path)
         super().__init__(msg)
 
 

dvc/scm/__init__.py

@@ -1,4 +1,4 @@
-"""Manages source control systems(e.g. Git)."""
+"""Manages source control systems (e.g. Git)."""
 
 from dvc.scm.base import Base
 from dvc.scm.git import Git

dvc/scm/base.py

@@ -1,4 +1,4 @@
-"""Manages source control systems(e.g. Git) in dvc."""
+"""Manages source control systems (e.g. Git) in DVC."""
 
 import os
 

scripts/completion/dvc.zsh

@@ -18,7 +18,7 @@ _dvc_commands() {
     "commit:Save changed data to cache and update DVC-files."
     "config:Get or set config settings."
     "destroy:Remove DVC-files, local DVC config and data cache."
-    "diff:Show changes between commits in the DVC repository, or between a commit and the workspace."
+    "diff:Show added, modified, or deleted data between commits in the DVC repository, or between a commit and the workspace."
     "fetch:Get files or directories tracked by DVC from remote storage into the cache."
     "get-url:Download or copy files from URL."
     "get:Download data from DVC repository."