Reword function description slightly

Use of the term "dotted-decimal" improves clarity. Put a full-stop where
one should have been.

Signed-off-by: David Horstmann <david.horstmann@arm.com>
diff --git a/include/mbedtls/oid.h b/include/mbedtls/oid.h
index 1d73506..5b75077 100644
--- a/include/mbedtls/oid.h
+++ b/include/mbedtls/oid.h
@@ -472,9 +472,9 @@
 int mbedtls_oid_get_numeric_string(char *buf, size_t size, const mbedtls_asn1_buf *oid);
 
 /**
- * \brief           Translate a string containing a numeric representation
- *                  of an ASN.1 OID into its encoded form
- *                  (e.g. "1.2.840.113549" into "\x2A\x86\x48\x86\xF7\x0D")
+ * \brief           Translate a string containing a dotted-decimal
+ *                  representation of an ASN.1 OID into its encoded form
+ *                  (e.g. "1.2.840.113549" into "\x2A\x86\x48\x86\xF7\x0D").
  *                  On success, this function allocates oid->buf from the
  *                  heap. It must be freed by the caller using mbedtls_free().
  *