merge(3p/git): Merge git subtree at v2.29.2

This also bumps the stable nixpkgs to 20.09 as of 2020-11-21, because
there is some breakage in the git build related to the netrc
credentials helper which someone has taken care of in nixpkgs.

The stable channel is not used for anything other than git, so this
should be fine.

Change-Id: I3575a19dab09e1e9556cf8231d717de9890484fb

third_party/git/Documentation/git-remote.txt

@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [verse]
 'git remote' [-v | --verbose]
-'git remote add' [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=<fetch|push>] <name> <url>
+'git remote add' [-t <branch>] [-m <master>] [-f] [--[no-]tags] [--mirror=(fetch|push)] <name> <url>
 'git remote rename' <old> <new>
 'git remote remove' <name>
 'git remote set-head' <name> (-a | --auto | -d | --delete | <branch>)
@@ -35,7 +35,7 @@ OPTIONS
 -v::
 --verbose::
 	Be a little more verbose and show remote url after name.
-	NOTE: This must be placed between `remote` and `subcommand`.
+	NOTE: This must be placed between `remote` and subcommand.
 
 
 COMMANDS
@@ -46,7 +46,7 @@ subcommands are available to perform operations on the remotes.
 
 'add'::
 
-Adds a remote named <name> for the repository at
+Add a remote named <name> for the repository at
 <url>.  The command `git fetch <name>` can then be used to create and
 update remote-tracking branches <name>/<branch>.
 +
@@ -109,13 +109,13 @@ With `-d` or `--delete`, the symbolic ref `refs/remotes/<name>/HEAD` is deleted.
 +
 With `-a` or `--auto`, the remote is queried to determine its `HEAD`, then the
 symbolic-ref `refs/remotes/<name>/HEAD` is set to the same branch. e.g., if the remote
-`HEAD` is pointed at `next`, "`git remote set-head origin -a`" will set
+`HEAD` is pointed at `next`, `git remote set-head origin -a` will set
 the symbolic-ref `refs/remotes/origin/HEAD` to `refs/remotes/origin/next`. This will
 only work if `refs/remotes/origin/next` already exists; if not it must be
 fetched first.
 +
-Use `<branch>` to set the symbolic-ref `refs/remotes/<name>/HEAD` explicitly. e.g., "git
-remote set-head origin master" will set the symbolic-ref `refs/remotes/origin/HEAD` to
+Use `<branch>` to set the symbolic-ref `refs/remotes/<name>/HEAD` explicitly. e.g., `git
+remote set-head origin master` will set the symbolic-ref `refs/remotes/origin/HEAD` to
 `refs/remotes/origin/master`. This will only work if
 `refs/remotes/origin/master` already exists; if not it must be fetched first.
 +
@@ -127,7 +127,7 @@ This can be used to track a subset of the available remote branches
 after the initial setup for a remote.
 +
 The named branches will be interpreted as if specified with the
-`-t` option on the 'git remote add' command line.
+`-t` option on the `git remote add` command line.
 +
 With `--add`, instead of replacing the list of currently tracked
 branches, adds to that list.
@@ -181,16 +181,16 @@ fetch --prune <name>`, except that no new references will be fetched.
 See the PRUNING section of linkgit:git-fetch[1] for what it'll prune
 depending on various configuration.
 +
-With `--dry-run` option, report what branches will be pruned, but do not
+With `--dry-run` option, report what branches would be pruned, but do not
 actually prune them.
 
 'update'::
 
 Fetch updates for remotes or remote groups in the repository as defined by
-remotes.<group>.  If neither group nor remote is specified on the command line,
+`remotes.<group>`. If neither group nor remote is specified on the command line,
 the configuration parameter remotes.default will be used; if
 remotes.default is not defined, all remotes which do not have the
-configuration parameter remote.<name>.skipDefaultUpdate set to true will
+configuration parameter `remote.<name>.skipDefaultUpdate` set to true will
 be updated.  (See linkgit:git-config[1]).
 +
 With `--prune` option, run pruning against all the remotes that are updated.