docs: Generate manpages from docs, use in CLI

Change-Id: I6a6a69646c6ff4c4b70cb928dc1df06890144429

cli/zilch-rust.scm

@@ -3,6 +3,9 @@
 (foreign-declare "#include \"stock_overrides.h\"")
 (define stock-overrides (foreign-value "stock_overrides" nonnull-c-string))
 
+(foreign-declare "#include \"man_rust.h\"")
+(define man-page (foreign-value "man_rust" nonnull-c-string))
+
 (define get-cpu-count
   (foreign-lambda* int ()
     "cpu_set_t set; sched_getaffinity(0, sizeof(set), &set); C_return(CPU_COUNT(&set));"))
@@ -10,30 +13,7 @@
 (define (print-help msg)
   (when msg
     (write-string (string-append msg "\n\n") (current-error-port)))
-  (write-string "Usage: zilch-cli-rust [OPTION] [TARGET...]
-Process the given crate directory (or the current directory, if unspecified)
-and output derivations for each target given on the command line (or all
-executables in the crate, if unspecified)
-
-  -h, --help              Print this help message.
-  -j, --max-jobs COUNT    The maximum amount of builds to run. Defaults
-                          to the amount of cores.
-  -v, --verbose           Increase the verbosity configured in the Nix
-                          daemon.
-  -L, --print-build-logs  Print derivation logs as they come in.
-  -m, --crate-dir DIR     The directory to use as root crate.
-  -r, --replace DIR       Replace the crate specified by the Cargo.toml
-                          with this source directory, rather than using
-                          the upstream crate. Can be specified more
-                          than once.
-  -z, --overrides PATH    Read build script overrides from this file.
-                          By default, a stock set of overrides is read.
-                          This can be disabled by passing `-z \"\"`
-                          (a blank string).
-
-   --debug                Crash on the first error, rather than
-                          continuing with the next package.
-" (current-error-port))
+  (write-string man-page (current-error-port))
   (exit (or (not msg) 1)))
 
 (define-values (options args)