manuals: fix name capitalization issues

- Using "BitBake" instead of "Bitbake" or "bitbake", aligning with the
  title of the "BitBake User Manual".
- Using "OpenEmbedded" instead of "Openembedded"
- Using "Python" instead of "python"

(From yocto-docs rev: 0b893e2a15aefedd7100445fc9d7eeed07b6afc6)

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

documentation/sphinx/yocto-vars.py

@@ -13,7 +13,7 @@ try:
     import yaml
 except ImportError:
     sys.stderr.write("The Yocto Project Sphinx documentation requires PyYAML.\
-    \nPlease make sure to install pyyaml python package.\n")
+    \nPlease make sure to install pyyaml Python package.\n")
     sys.exit(1)
 
 __version__  = '1.0'