config: document read_early_config() and read_very_early_config()

It's not clear what `read_early_config()` and `read_very_early_config()`
do differently compared to `repo_read_config()` from just looking at
their names. Document both of these in the header file to clarify their
intent.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

config.c

@@ -2234,10 +2234,6 @@ void read_early_config(config_fn_t cb, void *data)
 	strbuf_release(&gitdir);
 }
 
-/*
- * Read config but only enumerate system and global settings.
- * Omit any repo-local, worktree-local, or command-line settings.
- */
 void read_very_early_config(config_fn_t cb, void *data)
 {
 	struct config_options opts = { 0 };

config.h

@@ -192,7 +192,18 @@ int git_config_from_blob_oid(config_fn_t fn, const char *name,
 void git_config_push_parameter(const char *text);
 void git_config_push_env(const char *spec);
 int git_config_from_parameters(config_fn_t fn, void *data);
+
+/*
+ * Read config when the Git directory has not yet been set up. In case
+ * `the_repository` has not yet been set up, try to discover the Git
+ * directory to read the configuration from.
+ */
 void read_early_config(config_fn_t cb, void *data);
+
+/*
+ * Read config but only enumerate system and global settings.
+ * Omit any repo-local, worktree-local, or command-line settings.
+ */
 void read_very_early_config(config_fn_t cb, void *data);
 
 /**