Fix typos.

Co-authored-by: Jim Fehrle <jim.fehrle@gmail.com>
(cherry picked from commit e4c6451)

INSTALL.md

@@ -2,8 +2,8 @@ Installing From Sources
 =======================
 
 This document presents instructions to install this branch of Coq.
-For more general installation instructions and information about know
-build system issue, please consult the wiki page: 
+For more general installation instructions and information about known
+build system issues, please consult the wiki page: 
 
   https://github.com/coq/coq/wiki#coq-installation