Mention Both HRTB and Generic Lifetime in E0637 documentation

Also, small grammar fix.

compiler/rustc_error_codes/src/error_codes/E0637.md

@@ -1,5 +1,5 @@
 `'_` lifetime name or `&T` without an explicit lifetime name has been used
-on illegal place.
+in an illegal place.
 
 Erroneous code example:
 
@@ -13,7 +13,14 @@ fn underscore_lifetime<'_>(str1: &'_ str, str2: &'_ str) -> &'_ str {
     }
 }
 
-fn and_without_explicit_lifetime<T>()
+fn without_explicit_lifetime<T>()
+where
+    T: Iterator<Item = &u32>,
+                     //^ `&` without an explicit lifetime name
+{
+}
+
+fn without_hrtb<T>()
 where
     T: Into<&u32>,
           //^ `&` without an explicit lifetime name
@@ -40,9 +47,15 @@ fn underscore_lifetime<'a>(str1: &'a str, str2: &'a str) -> &'a str {
     }
 }
 
-fn and_without_explicit_lifetime<'foo, T>()
+fn without_explicit_lifetime<'a, T>()
 where
-    T: Into<&'foo u32>,
+    T: Iterator<Item = &'a u32>,
+{
+}
+
+fn without_hrtb<T>()
+where
+    T: for<'foo> Into<&'foo u32>,
 {
 }
 ```