Docs: Language fix to 01_compress_easy.c.

Thanks to Jonathan Nieder.

doc/examples/01_compress_easy.c

diff --git a/doc/examples/01_compress_easy.c b/doc/examples/01_compress_easy.c
index f79cade..e6dd2b0 100644
--- a/doc/examples/01_compress_easy.c
+++ b/doc/examples/01_compress_easy.c
@@ -27,7 +27,7 @@
 {
 	fprintf(stderr, "Usage: %s PRESET < INFILE > OUTFILE\n"
 			"PRESET is a number 0-9 and can optionally be "
-			"by `e' to indicate extreme preset\n",
+			"followed by `e' to indicate extreme preset\n",
 			argv0);
 	exit(EXIT_FAILURE);
 }