Re-add missing "Prerequisites" header and fix typo
Patch from HARUYAMA Seigo <haruyama at unixuser org>.
diff --git a/INSTALL b/INSTALL
index 6bc80b6..92106bf 100644
--- a/INSTALL
+++ b/INSTALL
@@ -1,3 +1,4 @@
+1. Prerequisites
----------------
A C compiler. Any C89 or better compiler should work. Where supported,
@@ -231,7 +232,7 @@
ssh-keygen -t [type] -f /etc/ssh/ssh_host_key -N ""
-for each of the types you wish to generate (rsa, dsa or ecdsaa) or
+for each of the types you wish to generate (rsa, dsa or ecdsa) or
ssh-keygen -A