log: add some documentation

The `jj log` command had basically no documentation. Let's at least
start adding some.

cli/src/commands/log.rs

@@ -27,14 +27,18 @@ use crate::diff_util::{self, DiffFormatArgs};
 use crate::graphlog::{get_graphlog, Edge};
 use crate::ui::Ui;
 
-/// Show commit history
+/// Show revision history
+///
+/// Renders a graphical view of the project's history with, ordered with
+/// children before parents. By default, the output only includes mutable
+/// revisions, along with some additional revisions for context.
 #[derive(clap::Args, Clone, Debug)]
 pub(crate) struct LogArgs {
     /// Which revisions to show. Defaults to the `revsets.log` setting, or
     /// `@ | ancestors(immutable_heads().., 2) | trunk()` if it is not set.
     #[arg(long, short)]
     revisions: Vec<RevisionArg>,
-    /// Show commits modifying the given paths
+    /// Show revisions modifying the given paths
     #[arg(value_hint = clap::ValueHint::AnyPath)]
     paths: Vec<String>,
     /// Show revisions in the opposite order (older revisions first)

cli/tests/cli-reference@.md.snap

@@ -118,7 +118,7 @@ To get started, see the tutorial at https://github.com/martinvonz/jj/blob/main/d
 * `git` — Commands for working with the underlying Git repo
 * `init` — Create a new repo in the given directory
 * `interdiff` — Compare the changes of two commits
-* `log` — Show commit history
+* `log` — Show revision history
 * `move` — Move changes from one revision into another
 * `new` — Create a new, empty change and (by default) edit it in the working copy
 * `next` — Move the current working copy commit to the next child revision in the
@@ -1010,13 +1010,15 @@ This excludes changes from other commits by temporarily rebasing `--from` onto `
 
 ## `jj log`
 
-Show commit history
+Show revision history
+
+Renders a graphical view of the project's history with, ordered with children before parents. By default, the output only includes mutable revisions, along with some additional revisions for context.
 
 **Usage:** `jj log [OPTIONS] [PATHS]...`
 
 ###### **Arguments:**
 
-* `<PATHS>` — Show commits modifying the given paths
+* `<PATHS>` — Show revisions modifying the given paths
 
 ###### **Options:**