Fix RST rendering and other typos

1) One space was missing from the indentation and, hence, rendering error
was generated in the user guide.
2) Partially reword Pointer Authentication related info.

Change-Id: Id5e65d419ec51dd7764f24d1b96b6c9942d63ba4
Signed-off-by: John Tsichritzis <john.tsichritzis@arm.com>

docs/user-guide.rst

@@ -359,12 +359,17 @@ Common build options
    registers to be included when saving and restoring the CPU context. Default
    is 0.
 
--  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, enables
-   Pointer Authentication for Secure world. This will cause the ARMv8.3-PAuth
-   registers to be included when saving and restoring the CPU context as
-   part of world switch. Default value is 0 and this is an experimental feature.
-   Note that Pointer Authentication is enabled for Non-secure world irrespective
-   of the value of this flag if the CPU supports it.
+-  ``CTX_INCLUDE_PAUTH_REGS``: Boolean option that, when set to 1, allows
+   Pointer Authentication for **Secure world**. This will cause the
+   Armv8.3-PAuth registers to be included when saving and restoring the CPU
+   context as part of a world switch. Default value is 0. Pointer Authentication
+   is an experimental feature.
+
+   Note that, if the CPU supports it, Pointer Authentication is allowed for
+   Non-secure world irrespectively of the value of this flag. "Allowed" means
+   that accesses to PAuth-related registers or execution of PAuth-related
+   instructions will not be trapped to EL3. As such, usage or not of PAuth in
+   Non-secure world images, depends on those images themselves.
 
 -  ``DEBUG``: Chooses between a debug and release build. It can take either 0
    (release) or 1 (debug) as values. 0 is the default.
@@ -417,12 +422,12 @@ Common build options
    partitioning in EL3, however. Platform initialisation code should configure
    and use partitions in EL3 as required. This option defaults to ``0``.
 
--  ``ENABLE_PAUTH``: Boolean option to enable ARMv8.3 Pointer Authentication
-  support for TF-A BL images itself. If enabled, it is needed to use a compiler
-  that supports the option ``-msign-return-address``. This flag defaults to 0
-  and this is an experimental feature.
-  Note that Pointer Authentication is enabled for Non-secure world irrespective
-  of the value of this flag if the CPU supports it.
+-  ``ENABLE_PAUTH``: Boolean option to enable Armv8.3 Pointer Authentication
+   for **TF-A BL images themselves**. If enabled, the compiler must support the
+   ``-msign-return-address`` option. This flag defaults to 0. Pointer
+   Authentication is an experimental feature.
+
+   If this flag is enabled, ``CTX_INCLUDE_PAUTH_REGS`` must also be enabled.
 
 -  ``ENABLE_PIE``: Boolean option to enable Position Independent Executable(PIE)
    support within generic code in TF-A. This option is currently only supported