Fix typo in bsrn.py doc string

Co-authored-by: Kevin Anderson <[email protected]>

Author: AdamRJensen

pvlib/iotools/bsrn.py

@@ -27,7 +27,8 @@ def read_bsrn(filename):
     global, diffuse, direct and downwelling long-wave radiation [2]_. Future
     updates may include parsing of additional data and meta-data.
 
-    BSRN files are freely avaiable and can be accessed via FTP [3]_. Required
+    BSRN files are freely available and can be accessed via FTP [3]_. Required
+
     username and password are easily obtainable as described in the BSRN's
     Data Release Guidelines [4]_.