updated Crypto.md and added information to Building.md

doc/Building.md

@@ -129,10 +129,10 @@ Please do no forget to `make clean` after (re-)configuration and before building
 
 In addition to the built-in LZO1x for payload compression (`-z1` at the edge's commandline), n2n optionally supports [ZSTD](https://github.com/facebook/zstd). As of 2020, it is considered cutting edge and [praised](https://en.wikipedia.org/wiki/Zstandard) for reaching the currently technologically possible Pareto frontier in terms of CPU power versus compression ratio. ZSTD support can be configured using
 
-`./configure -- with-zstd`
+`./configure --with-zstd`
 
 which then will include ZSTD if found on the system. It will be available via `-z2` at the edges. Of course, it can be combined with the other features mentioned above:
 
-`./configure --with-openssl --with-zstd CFLAGS="-O3 -march=native"`
+`./configure --with-zstd --with-openssl CFLAGS="-O3 -march=native"`
 
-Again, please do no forget to `make clean` after (re-)configuration and before building (again) using `make` – can't reiterate often enough.
+Again, this cannot be reiterated often enough, please do no forget to `make clean` after (re-)configuration and before building (again) using `make`.