Add USE keyspace to documentation book
# USE keyspace
+Using a keyspace allows to omit keyspace name in queries.
+
+For example in `cqlsh` one could write:
+```sql
+cqlsh> SELECT * FROM my_keyspace.table;
+
+ a | b |
+-------+-------+
+ 12345 | 54321 |
+
+(1 rows)
+cqlsh> USE my_keyspace;
+cqlsh:my_keyspace> SELECT * FROM table;
+
+ a | b |
+-------+-------+
+ 12345 | 54321 |
+
+(1 rows)
+
+```
+Tables from other keyspaces can still easily be accessed by using their keyspace names.
+```sql
+cqlsh:my_keyspace> SELECT * FROM other_keyspace.other_table;
+```
+
+In the driver this can be achieved using `Session::use_keyspace`:
+```rust
+# extern crate scylla;
+# use scylla::Session;
+# use std::error::Error;
+# async fn check_only_compiles(session: &Session) -> Result<(), Box<dyn Error>> {
+session
+ .query("INSERT INTO my_keyspace.tab (a) VALUES ('test1')", &[])
+ .await?;
+
+session.use_keyspace("my_keyspace", false).await?;
+
+// Now we can omit keyspace name in the query
+session
+ .query("INSERT INTO tab (a) VALUES ('test2')", &[])
+ .await?;
+# Ok(())
+# }
+```
+
+The first argument is the keyspace name.
+The second argument states whether this name is case sensitive.
+
+### Multiple use queries at once
+Don't run multiple `use_keyspace` queries at once.
+This could end up with half of connections using one keyspace and the other half using the other.
+
+### Case sensitivity
+
+In CQL a keyspace name can be case insensitive (without `"`) or case sensitive (with `"`).
+If the second argument to `use_keyspace` is set to `true` this keyspace name will be wrapped in `"`.
+It is best to avoid the problem altogether and just not create two keyspaces with the same name but different cases.
+
+Let's see what happens when there are two keyspaces with the same name but different cases: `my_keyspace` and `MY_KEYSPACE`:
+
+```rust
+# extern crate scylla;
+# use scylla::Session;
+# use std::error::Error;
+# async fn check_only_compiles(session: &Session) -> Result<(), Box<dyn Error>> {
+// lowercase name without case sensitivity will use my_keyspace
+session.use_keyspace("my_keyspace", false).await?;
+
+// lowercase name with case sensitivity will use my_keyspace
+session.use_keyspace("my_keyspace", true).await?;
+
+// uppercase name without case sensitivity will use my_keyspace
+session.use_keyspace("MY_KEYSPACE", false).await?;
+
+// uppercase name with case sensitivity will use MY_KEYSPACE
+session.use_keyspace("MY_KEYSPACE", true).await?;
+# Ok(())
+# }
+```
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