Improve some comments, fix some typos
diff --git a/include/mbedtls/x509_crt.h b/include/mbedtls/x509_crt.h
index f4bc746..b7fd9e0 100644
--- a/include/mbedtls/x509_crt.h
+++ b/include/mbedtls/x509_crt.h
@@ -287,7 +287,7 @@
  *                 chaining up to those CAs will be trusted, and (2)
  *                 self-signed end-entity certificates to be trusted (for
  *                 specific peers you know) - in that case, the self-signed
- *                 certificate doens't need to have the CA bit set.
+ *                 certificate doesn't need to have the CA bit set.
  *
  * \param crt      a certificate (chain) to be verified
  * \param trust_ca the list of trusted CAs (see note above)