worktree: use 'worktree' over 'working tree'

It is helpful to distinguish between a 'working tree' and a 'worktree'.
A worktree contains a working tree plus additional metadata. This
metadata includes per-worktree refs and worktree-specific config.

This is the fifth of multiple changes to git-worktree.txt, restricted to
the CONFIGURATION FILE section.

While here, clear up some language to improve readability.

Helped-by: Taylor Blau <[email protected]>
Signed-off-by: Derrick Stolee <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: derrickstolee

Documentation/git-worktree.txt

@@ -284,13 +284,13 @@ which will handle refs correctly.
 
 CONFIGURATION FILE
 ------------------
-By default, the repository `config` file is shared across all working
-trees. If the config variables `core.bare` or `core.worktree` are
-present in the common config file and `extensions.worktreeConfig` is
-disabled, then they will be applied to the main working tree only.
+By default, the repository `config` file is shared across all worktrees.
+If the config variables `core.bare` or `core.worktree` are present in the
+common config file and `extensions.worktreeConfig` is disabled, then they
+will be applied to the main worktree only.
 
-In order to have configuration specific to working trees, you can turn
-on the `worktreeConfig` extension, e.g.:
+In order to have worktree-specific configuration, you can turn on the
+`worktreeConfig` extension, e.g.:
 
 ------------
 $ git config extensions.worktreeConfig true
@@ -303,16 +303,16 @@ versions will refuse to access repositories with this extension.
 
 Note that in this file, the exception for `core.bare` and `core.worktree`
 is gone. If they exist in `$GIT_DIR/config`, you must move
-them to the `config.worktree` of the main working tree. You may also
-take this opportunity to review and move other configuration that you
-do not want to share to all working trees:
+them to the `config.worktree` of the main worktree. You may also take this
+opportunity to review and move other configuration that you do not want to
+share to all worktrees:
 
  - `core.worktree` should never be shared.
 
  - `core.bare` should not be shared if the value is `core.bare=true`.
 
- - `core.sparseCheckout` is recommended per working tree, unless you
-   are sure you always use sparse checkout for all working trees.
+ - `core.sparseCheckout` should not be shared, unless you are sure you
+   always use sparse checkout for all worktrees.
 
 See the documentation of `extensions.worktreeConfig` in
 linkgit:git-config[1] for more details.