Update HOWTO.md

AY38910 register table error. The envelope bit is 4 and not 5

Author: mvac7

README.md

@@ -9,6 +9,7 @@ Programming language: C and Z80 assembler
 
 
 ---
+
 ## Description
 
 Library functions for access to internal or external MSX PSG AY-3-8910.

docs/HOWTO.md

@@ -371,13 +371,13 @@ coming soon...
 <td align=center>B</td><td align=center>A</td>
 </tr>
 <tr>
-<td>R8</td><td>Channel A Amplitude</td><td colspan=2></td><td align=center>Env</td><td colspan=5 align=center>Amplitude</td>
+<td>R8</td><td>Channel A Amplitude</td><td colspan=3></td><td align="center">Env</td><td colspan=4 align="center">Amplitude</td>
 </tr>
 <tr>
-<td>R9</td><td>Channel B Amplitude</td><td colspan=2></td><td align=center>Env</td><td colspan=5 align=center>Amplitude</td>
+<td>R9</td><td>Channel B Amplitude</td><td colspan=3></td><td align="center">Env</td><td colspan=4 align="center">Amplitude</td>
 </tr>
 <tr>
-<td>R10</td><td>Channel C Amplitude</td><td colspan=2></td><td align=center>Env</td><td colspan=5 align=center>Amplitude</td>
+<td>R10</td><td>Channel C Amplitude</td><td colspan=3></td><td align="center">Env</td><td colspan=4 align="center">Amplitude</td>
 </tr>
 <tr>
 <td>R11</td><td rowspan=2>Envelope Period</td><td colspan=8 align=center>8-Bit Fine Tune Envelope</td>