binman: Use a private directory for bintools

At present binman writes tools into the ~/bin directory. This is
convenient but some may be concerned about downloading unverified
binaries and running them. Place then in a special ~/.binman-tools
directory instead.

Mention this in the documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>

tools/binman/bintool.py

@@ -52,7 +52,7 @@ class Bintool:
     missing_list = []
 
     # Directory to store tools
-    tooldir = os.path.join(os.getenv('HOME'), 'bin')
+    tooldir = os.path.join(os.getenv('HOME'), '.binman-tools')
 
     def __init__(self, name, desc, version_regex=None, version_args='-V'):
         self.name = name