Docs: Add requirement of librsvg2-bin for doc generation

Require tool librsvg2-bin in docs for user guide generation.

librsvg2-bin shall be installed to support
sphinxcontrib-svg2pdfconverter.
Otherwise, user guide build will throw out warnings that RSVG converter
command 'rsvg-convert' cannot be run.

Change-Id: Ic988b2771c0c5317b130bb37696c1c2833c162f7
Signed-off-by: David Hu <david.hu@arm.com>
diff --git a/docs/getting_started/tfm_getting_started.rst b/docs/getting_started/tfm_getting_started.rst
index 1fddbb0..4e32ec3 100644
--- a/docs/getting_started/tfm_getting_started.rst
+++ b/docs/getting_started/tfm_getting_started.rst
@@ -367,6 +367,7 @@
    "Java runtime environment (JRE)",">1.8","Reference Manual, User Guide"
    "LaTex",,"pdf version of Reference Manual and User Guide"
    "PdfLaTex",,"pdf version of Reference Manual and User Guide"
+   "librsvg2-bin",, "User Guide"
 
 Dependency chain:
 
@@ -399,6 +400,7 @@
     state LaTex as "LaTex" <<pdf>>
     state PdfLaTex as "PdfLaTex" <<<<pdf>>>>
     state Doxygen as "Doxygen" <<doc>>
+    state librsvg as "librsvg2-bin" <<doc>>
 
     [*] --> fw
     fw --> c_comp
@@ -431,6 +433,7 @@
     tabs --> Python3
     sphnix_puml --> Python3
     sphnix_svg --> Python3
+    sphnix_svg --> librsvg
     Sphinx --> PlantUML
     PlantUML --> JRE
     PlantUML --> gwiz
diff --git a/docs/technical_references/instructions/documentation_generation.rst b/docs/technical_references/instructions/documentation_generation.rst
index da21dee..e6b4fc5 100644
--- a/docs/technical_references/instructions/documentation_generation.rst
+++ b/docs/technical_references/instructions/documentation_generation.rst
@@ -127,6 +127,8 @@
     - Java runtime environment 1.8 or later (for running PlantUML)
     - LaTeX - for PDF generation only
     - PdfLaTeX - for PDF generation only
+    - librsvg2-bin - a SVG pictures renderer library to support
+      sphinxcontrib-svg2pdfconverter
 
 .. tabs::