Document why/how to deal with filehandling max limitation on Linux

[kelson42]

Following #289

[kelson42]

After discussion which should be able to implement a solution to:

• Save files smaller than cluster size in memory
• Keep filehandle open for bigger files

[ghost]

How do I work around the "Too many open files" error?

[mgautierfr]

run ulimit -n 2048 before running zimwriterfs to change the limit of open files to 2048 (or more, the default value is 1024)

[ghost]

run ulimit -n 2048 before running zimwriterfs to change the limit of open files to 2048 (or more, the default value is 1024)

Thank you, this worked (well, a higher value than 2048, but it worked).