Add SquashFS block size hint to "Filesystem image too big" section

[mk-pmb]

The stable 2.0 says

ERROR: kernel image is ### bytes too big. See http://freetz.org/wiki/FAQ#Filesystemimagetoobig for details.

so let's add there as the first bullet

• Old versions of Freetz used to also link to this section for "ERROR: kernel image is ### bytes too big." If that is the error you're debugging, have a look at the next section.

• Alte Versionen von Freetz verlinken diesen Abschnitt auch für "ERROR: kernel image is ### bytes too big." Im Falle dieser Meldung, siehe nächster Abschnitt.

and then add a secion

ERROR: kernel image is … too big.

• In case your kernel image is just a few (kilo)bytes too big and luck is on your side, it might be fixable by changing "SquashFS options ---> SquashFS block size". With smaller blocks, less space is wasted for empty space behind the end of files that don't fit tightly. However, for big files, smaller blocks means you need more of them, and thus more index entries pointing to the blocks. The goal is to find a good balance between wasting space on unused parts of blocks, and wasting space on lots of index entries.

ERROR: kernel image is … too big.

• Wenn das Kernelabbild nur wenige (Kilo)Bytes zu groß ist und du Glück hast, kann es helfen, eine andere Blockgröße für SquashFS auszuwählen (bei SquashFS options ---> SquashFS block size). Kleinere Blöcke erzeugen weniger Verschnitt (ungenutzter Restspeicherplatz im letzten Block einer Datei), verbrauchen dafür allerdings mehr Speicherplatz für Katalogdaten. Es gilt daher, die richtige Balance zu finden zwischen Verschnitt und Katalogdaten.

Are the HTML files the authoritative source for the wiki page texts, i.e. shall I modify the HTML directly? I could provide a PR for that.