[PATCH] doc: builtin add -i is enabled by feature.experimental

[Todd Zullinger <tmz@pobox.com>]

Note that add.interactive.useBuiltin is enabled by feature.experimental.
It was added in 2df2d81ddd (add -i: use the built-in version when
feature.experimental is set, 2020-09-08).

Signed-off-by: Todd Zullinger <tmz@pobox.com>
---
I was checking my configuration to see if I still needed to have
add.interactive.useBuiltin set and noticed that it wasn't listed in the
settings enabled by feature.experimental.

Unless it's time to take this out of the experimental phase, it seems worth
documenting -- if for no other reason than to keep fetch.negotiationAlgorithm
from being lonely in the feature.experimental section. ;)

FWIW, I've had this enabled for perhaps a year or so and I don't recall any
instances where it hasn't worked well.  It has come in handy on some systems
where I can't easily install Perl but don't want to give up `add -[ip]`.
Thanks Dscho!

 Documentation/config/add.txt     | 3 ++-
 Documentation/config/feature.txt | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/Documentation/config/add.txt b/Documentation/config/add.txt
index c9f748f81c..7d6d325571 100644
--- a/Documentation/config/add.txt
+++ b/Documentation/config/add.txt
@@ -9,4 +9,5 @@ add.ignore-errors (deprecated)::
 add.interactive.useBuiltin::
 	[EXPERIMENTAL] Set to `true` to use the experimental built-in
 	implementation of the interactive version of linkgit:git-add[1]
-	instead of the Perl script version. Is `false` by default.
+	instead of the Perl script version.  If `feature.experimental` is
+	enabled, this setting is `true`.  By default, it is `false`.
diff --git a/Documentation/config/feature.txt b/Documentation/config/feature.txt
index cdecd04e5b..caaa97dc61 100644
--- a/Documentation/config/feature.txt
+++ b/Documentation/config/feature.txt
@@ -12,6 +12,10 @@ feature.experimental::
 	setting if you are interested in providing feedback on experimental
 	features. The new default values are:
 +
+* `add.interactive.useBuiltin=true` which enables the built-in implementation
+of the interactive version of linkgit:git-add[1] instead of the Perl script
+version.
++
 * `fetch.negotiationAlgorithm=skipping` may improve fetch negotiation times by
 skipping more commits at a time, reducing the number of round trips.
 
 feature.manyFiles::
 	Enable config options that optimize for repos with many files in the
-- 
2.32.0