Repository: iterative/dvc
Pull request: ui: '-j' option now mentions docs
Fixes #1310 

* [x] ❗ I have followed the [Contributing to DVC](https://dvc.org/doc/user-guide/contributing/core) checklist.

* [ ] 📖 If this PR requires [documentation](https://dvc.org/doc) updates, I have created a separate PR (or issue, at least) in [dvc.org](https://github.com/iterative/dvc.org) and linked it here.

I don't think that documentation should be updated.


Problem statement:
Improve `-j` help messages 
For example, `dvc gc -j N`. There are also other DVC commands that have this option.

`-j` specifies parallelism level for the command. 

It should specify that default number depends on a remote type and that to get defaults one should refer to docs.

Hints from issue discussion:
It now reads "Number of jobs to run simultaneously." Is that better?

And is this a `p3`?
@jorgeorpinel I think the idea was to include something like "Refer to docs to get default value that depends on the remote type" (better written). 
1. As far as I understand default value depends not only on remote type but also on hardware configuration.
1. It seems that short help messages are more desirable than long ones.

So why not just "Refer to docs to get default value"?

Commit message: ui: '-j' option now mentions docs

Patch to review:
diff --git a/dvc/command/data_sync.py b/dvc/command/data_sync.py
index 5b931177ec..e00b411ab8 100644
--- a/dvc/command/data_sync.py
+++ b/dvc/command/data_sync.py
@@ -97,7 +97,8 @@ def shared_parent_parser():
         "-j",
         "--jobs",
         type=int,
-        help="Number of jobs to run simultaneously.",
+        help="Number of jobs to run simultaneously. "
+        "Refer to docs to get default value.",
         metavar="<number>",
     )
     parent_parser.add_argument(
diff --git a/dvc/command/gc.py b/dvc/command/gc.py
index b1fa32fdb1..8bd1ac5d75 100644
--- a/dvc/command/gc.py
+++ b/dvc/command/gc.py
@@ -123,7 +123,8 @@ def add_parser(subparsers, parent_parser):
         "-j",
         "--jobs",
         type=int,
-        help="Number of jobs to run simultaneously.",
+        help="Number of jobs to run simultaneously. "
+        "Refer to docs to get default value.",
         metavar="<number>",
     )
     gc_parser.add_argument(


Code review comments:
diff_hunk: @@ -97,7 +97,8 @@ def shared_parent_parser():
         "-j",
         "--jobs",
         type=int,
-        help="Number of jobs to run simultaneously.",
+        help="Number of jobs to run simultaneously. "
+        "Refer to docs to get default value.",
path: dvc/command/data_sync.py
text: @user1:
Maybe let's just copypaste from docs? E.g. from https://dvc.org/doc/command-reference/push
```
The default value is 4 * cpu_count(). For SSH remotes, the default is 4. Using more jobs may improve the overall transfer speed.
```

@author:
I've noticed that most help messages are short (2 sentences max) so I decided to use "refer to docs...". However, I have no strong opinion in that regard. If it's fine to have long messages I can copy text from cmd ref.

@user1:
Yes, there is no limit for the help messages. We could totally copypaste those two sentences :) Thank you! :pray: 

@author:
I've updated message