Fix typo

Author: jyn514

src/building/bootstrapping.md

@@ -96,7 +96,7 @@ Because there are two separate codebases behind `x.py`, they need to
 be kept in sync. In particular, both `bootstrap.py` and the bootstrap binary
 parse `config.toml` and read the same command line arguments. `bootstrap.py`
 keeps these in sync by setting various environment variables, and the
-programs sometimes to have add arguments that are explicitly ignored, to be
+programs sometimes have to add arguments that are explicitly ignored, to be
 read by the other.
 
 ### Adding a setting to config.toml