Update README: installation instructions (#281)

The readme installation instructions contain a command that does not work for some of the packages lcov depends on.
For instance, trying to install `Scalar::Util` as per current suggested command (perl -MCPAN -e "install Scalar::Util") will result in: 
Can't locate object method "install" via package "Scalar::Util" at -e line 1.

Signed-off-by: Rostyslav Skrypnyk <[email protected]>

Author: bytebunny

README

@@ -140,7 +140,7 @@ These perl packages include:
 If your system is missing any of these, then you may be able to install them
 via:
 
-   $ perl -MCPAN -e 'install "packageName"'
+   $ perl -MCPAN -e 'install(<packageName>)'
 
 You will very likely need superuser access to be able to install Perl
 modules.