spelling error in README.rst

[JamesMichealJohnson]

The word "install" is spelt as "isntall"

change

Note that running make install will install a desktop entry file, in either "system" or "user" mode. This can be specified via the MODE make variable (the default is "user"). To isntall the desktop entry for the all users, use:

to

Note that running make install will install a desktop entry file, in either "system" or "user" mode. This can be specified via the MODE make variable (the default is "user"). To install the desktop entry for the all users, use: